Retinoblastoma major review with updates on Middle East management protocols

Abstract

Many advances in the field of management of retinoblastoma emerged in the past few years. Patterns of presentation of retinoblastoma in the Middle East region differ from Western community. The use of enucleation as a radical method of eradicating advanced disease is not easily accepted by patient’s family. We still do see stage E, failed or resistant retinoblastoma and advanced extraocular disease ensues as a result of delayed enucleation decision. In this review, we discuss updates in management of retinoblastoma with its implication on patients in our part of the world. Identifying clinical and high risk characteristics is important prognostically and are discussed for further management of retinoblastoma cases.

Introduction

Retinoblastoma is the commonest primary ocular malignancy of childhood originating from primitive retinoblasts with tendency towards cone differentiation. Retinoblasts arise from the inner neuroepithelial layers of the embryonic optic cup.¹ The incidence of retinoblastoma ranges from 1/15,000 to 1/20,000 live births with an annual incidence in children younger than 5 years of 10.9/million. Two distinct forms of retinoblastoma are present namely sporadic and familial (Table 1). Most presenting cases are unilateral sporadic. Only 33% of cases are bilateral and all (100%) are hereditary while 15% of unilateral cases presenting with unilateral multifocal tumors are hereditary. Familial cases represent 10% of cases and 90% of cases are presenting before age 4 years.^1,2 In Egypt, after reviewing 321 new cases of retinoblastoma over 5 years at the National Eye Center and the Eye and Laser World Center, the estimated number of new retinoblastoma cases is 100–120 cases/year.³ In a recent report from Jordan, the mean age-adjusted incidence of retinoblastoma was 9.32 cases per million children per year for children aged 0–5 years.⁴ Retinoblastoma constituted 4.8% of childhood cancer treated over 10 years at the National Cancer Institute in Sudan and presented in an advanced stage in 16 out of 25 reported cases.⁵

Table 1.

Main differences between sporadic and familial retinoblastoma.

	Sporadic retinoblastoma	Familial retinoblastoma
Incidence	90%	5–10%
	1/100,000 child
Mean age of presentation (months)	30	12
Mutation	Somatic: the mutation is only in retinoblasts	Germline: the mutation is in normal cells in the body and in retinoblasts
Laterality	Unilateral unifocal	Bilateral 70%
		May be unilateral but multifocal 30%
Second cancers	No higher risk	Increased risk
Genetic transmission	No	Yes

Genetics

To properly understand the role of retinoblastoma gene, it is important to revisit the normal cell cycle which represents the different phases of cell proliferation. Most cells of the body are in a G0 phase which is a quiescent phase where cells contain active hypophosphorylated form of retinoblastoma protein. When there is need for cell division, the cells go into G1 phase which is a presynthetic growth phase 1 where the cells contain active hypophosphorylated form of retinoblastoma protein. S phase is a DNA-synthetic phase. G2 phase is a premitotic growth phase 2. M phase is a mitotic phase resulting in duplication of the dividing cell.⁶

Cyclins are regulatory proteins controlling the cell cycle. Their regulatory function is accomplished by binding and activating CDKs (cyclin dependent kinases). CDKs control the important transition points in cell cycle through phosphorylation or dephosphorylation of other proteins. Cyclin-CDK complexes are regulated by the binding of CDK inhibitors which are important in regulating cell cycle check points from G1 to S phase.^6–8 At this checkpoint, the cell ensures a flawless DNA replication with all errors repaired before progression to cell division. This checkpoint is guarded by retinoblastoma protein in its active hypophosphorylated form (Fig. 1). Tumor virus transforming proteins (adenovirus EIA, simian virus 40 (SV40) antigen, large T and human papilloma virus [HPV-E7]) induce tumors by binding to and inactivating the active form of Rb protein.⁹ Some oncoviruses (SV4O, HPV, adenovirus) are thought to produce cancer by making proteins that complex and inactivates the suppressor protein product of the RB gene.¹⁰ The Rb protein unable to bind to E2F transcription factor is functionally deleted with subsequent loss of cellular ability to be inhibited by antigrowth signals (Fig. 2). Additionally, RB primary tumors harbor cells with expression of stem cell markers namely CD44 and retinal progenitor markers, PROX1 and syntaxin 1A.¹¹ Presence of these neural stem cells among others could make the tumor more aggressive in behavior or metastases, reactive after a quiescent dormant period or more resistant to anticancer therapy.¹²

Figure 1.

Growth cycle: most cells of the body are in G0 or quiescent stage. When they start cell division, they pass through G1, S, G2 and M phases. Retinoblastoma protein (Rb) in its active hypophosphorylated form acts on the checkpoint from G1 to S phase to ensure flawless DNA replication.

Figure 2.

Inactivation of Rb protein by hyperphosphorylation results in uncontrolled cell replication.

The ability of the tumor to be invasive may be explained by the presence of expression of endothelial nitic acid synthases (eNOS) and specially the inducible nitric acid synthases (iNOS).¹³ Degradation of basement membrane by matrix metalloproteinases (MMPs) is one of the most critical steps in various stages of tumor progression, including tumor angiogenesis, tumor growth, and also local invasion and subsequent distant metastasis.¹⁴ Adithi et al.¹⁵ have demonstrated higher expressions of EMMPRIN, MMP-2 and MMP-9, and TIMP-1 and TIMP-2 in invasive RB tumors. Poorly differentiated tumors showed higher expression of MMP-2 than tumors that were moderately or well-differentiated tumors. The expression of TIMP-1 and TIMP-2 was higher in invasive tumors. With respect to differentiation, there were higher expressions of TIMP-1 and TIMP-2 in poorly differentiated tumors, as compared to moderately and well-differentiated tumors. Epithelial cell adhesion molecule (EpCAM) is highly expressed in RB tumors with invasion compared to tumors without invasion.¹⁶ EpCAM plays a role in increased cellular proliferation of RB cells and can be considered a potential target molecule in the therapeutic interventions for RB management. Protein 53 (p53) controls powerful stress response as it integrates upstream signals from many types of DNA damage and inappropriate oncogenic stimulation, all of which lead to p53 activation and subsequent regulation of genes involved in cell cycle arrest or apoptosis.¹⁷ Proteomics has contributed significantly in understanding the biology of RB tumors by revealing altered protein expression in tumor cells. The altered proteins belong to different categories such as apoptosis, cell proliferation, signal transduction, metabolic, and active transport processes. PRDX6 and CRYAA could be potential targets in the clinical management of RB.¹⁸

The retinoblastoma gene: a tumor suppressor anti-oncogene

Retinoblastoma (RB1) gene is located on the long arm of chromosome 13 (13q14 band). This gene is inherited as an autosomal dominant disease; however it is a “recessive tumor suppressor gene” at the cellular level. RB gene sequence contains 180,388 base pairs. The Rb gene protein product (928 amino acids) is a DNA-binding protein found in the nucleus of every cell in the body. The DNA-binding protein exists in an active hypophosphorylated and an inactive hyperphosphorylated state. Rb protein is involved in control of the cell cycle (necessary for terminal differentiation). When active, Rb protein prevents advancement of cells from G1 to S phase of the cell cycle (Fig. 1). When the cells are stimulated by growth factors, RB protein is inactivated by phosphorylation allowing the cells to go from G1 to S phase.^7,19 Once in S phase, cells are committed to divide without additional growth factor stimulation with lack of terminal differentiation meaning cancer development. Absence of RB protein or loss causes continual cell division into S phase with lack of terminal differentiation meaning cancer development and metastasis (Fig. 2). This requires inactivation of both copies of the RB1 gene.^20,21

Retinoblastoma gene inheritance

The retinoblastoma (RB) gene is inherited as an autosomal dominant disease. However at the cellular level it is a “recessive tumor suppressor gene”. Normal individuals have two functional copies of the RB gene (RB, RB). Familial cases are hemizygous for retinoblastoma gene (RB, rb) “first hit” containing one functional and one inactivated gene, in all cells of the body. A single functional gene prevents malignant transformation. Tumors develop when the “second hit” is acquired as a somatic event in the developing retinal cell, thus both normal suppressor genes in a single retinal cell are lost or inactivated (rb, rb). The absence of the gene product in the homozygous state leads to the development of retinoblastoma (rb, rb). In the hereditary form two mutations occur, in both a prezygotic cell and a postzygotic cell. First mutation occurs usually in a sperm or an ovum. All somatic cells are affected by the first hit. Second mutation occurs in a somatic retinal cells resulting in multifocal unilateral or bilateral disease or both (Fig. 3).¹ Second mutation may affect other cells of the body resulting in pineal tumors, sarcomas, breast and lung cancers.²² Tumors in cases of familial retinoblastoma are frequently bilateral multifocal or unilateral multicentric (15% of cases).

Figure 3.

Hereditary or genetic mutation starts in a sperm “first hit” (red chromosome in the sperm). This results in a zygote with loss of one allele of RB gene. A second hit (arrow) occurs in a retinoblast resulting in tumor formation. All cells of the body carry a hemizygote state of RB.

Sporadic somatic retinoblastoma result from the sequential inactivation of both genes in a single retinal cell in a patient whose genotype is normal (RB, RB). Both hits are acquired events (occur in a post-zygotic somatic cell), explaining the later onset and unilaterality of the disease.

It is important to counsel the family members affected by retinoblastoma about the probability of other family members affection by the disease and to emphasize the importance of early postnatal screening.¹ Genetic risk for affected siblings is presented in Table 2.

Table 2.

Genetic counseling: risk that subsequent child will have retinoblastoma.

Unilateral retinoblastoma
Affected parent with no affected children	3%
Normal parents, one affected child	3%
One affected parent, one affected child	30%
Bilateral retinoblastoma
One affected parent, no affected child	40%
Normal parents, one affected child	10%
One affected parent, one affected child	50%

Diagnosis

Ninety percent of retinoblastoma cases are presenting below the age of 4 years. Restriction fragment length polymorphisms performed on chorionic villus sampling or amniocentesis cultured cells.²³ Additionally, during in vitro fertilization, absence of preimplantation genetic diagnosis of retinoblastoma gene mutation allowed pregnancies of a fetus without retinoblastoma.²⁴

Diagnosis at 1 month of age is highly positive in absence of leucocoria in patients with family history of retinoblastoma whether a parent or a sibling is affected (Fig. 4A).²⁵

Figure 4.

Hereditary retinoblastoma diagnosed in the sibling at age 2 weeks OS. Child underwent chemoreduction with focal therapy. B: initial good response after laser transpupillary thermotherapy. C: Tumor recurrence. D: tumor ablation following Ruthenium-106 plaque application. Tumor controlled at 60 months follow up.

Typically, intraocular retinoblastoma manifests as leucocoria (90%) and strabismus (35%). More advanced disease presents with buphthalmos, fixed dilated pupil, spontaneous hyphema, NVG and heterochromia iridis. Flat retinoblastoma presents in elderly as a pseudohypopyon. When the tumor outgrows its blood supply and becomes necrotic, it presents as an orbital cellulitis-like picture. Extraocular retinoblastoma is still encountered in our part of the world mainly due to delay in diagnosis, delay in treatment and patients refusal of primary or secondary enucleation as a curative modality. Proptosis is related to an orbital tumor due to massive extrascleral extension or a fungating mass through corneal perforation. Preauricular and submandibular lymphadenopathy and systemic metastases involving bones, or bone marrow, meninges, paranasal sinuses, salivary glands, lymph nodes, subcutaneous tissue, liver, spleen, pleura, and testes.¹ A special entity of retinoblastoma is the trilateral retinoblastoma, where bilateral intraocular disease presents with a pineal gland tumor and suprasellar/parasellar neuroblastic tumors and primitive neuroectodermal tumor.²⁶ This is less commonly seen in the era of systemic chemotherapy use.²⁷

Another rare entity is the spontaneous regression or arrest of retinoblastoma which represents a tumor that undergoes spontaneous growth arrest and or involution leaving a partially calcified scar without any previous treatment. This tumor behaves genetically as hereditary retinoblastoma and follow up is warranted as the tumor may transform to actively growing retinoblastoma. Primary phthisical eyes harbouring retinoblastoma are often associated with bilateral disease. Enucleation of primary phthisical eyes is recommended as residual viable tumor cells with characteristics of poorly differentiated retinoblastoma was noted in a majority of cases.²⁸

High risk factors associated with retinoblastoma

It is important to identify high risk factors associated with retinoblastoma recurrence or metastasis. Clinical high risk factors include extensively necrotic retinoblastoma which is found to be associated with extraocular extension, optic nerve invasion, or choroidal invasion.²⁹ Older age, longer lag period, hyphema, pseudohypopyon, staphyloma, and orbital cellulitis are other important high risk factors.³⁰ Delay in enucleation of more than 3 months after diagnosis and the use of pre-enucleation chemotherapy in group E eyes with advanced retinoblastoma downstaged pathologic evidence of extraocular extension, and increased the risk of metastatic death from reduced surveillance and inappropriate management of high-risk disease.³¹ Elevated intraocular pressure and buphthalmos are also associated with high risk pathological features.³²

In submitting the enucleated globe for histopathology, the ophthalmic pathologist should comment on several high risk factors which have significant implications on patient survival. Pathological high risk factors include: Retinoblastoma with invasion into the postlaminar optic nerve and/or posterior uvea which is found to be a high risk for metastasis and death.³³ Retrolaminar optic nerve invasion and massive uveal invasion (defined as >3 mm in diameter), scleral invasion with iris neovascularization and neovascular glaucoma are other high risk factors (Fig. 5).³⁴ In presence of histopathological high risk factors, postenucleation chemotherapy use was effective in preventing metastasis.^33,35

Figure 5.

High risk factors with retinoblastoma. (A) Gross section showing massive choroidal invasion (>3 mm) with optic nerve invasion. (B) Photomicrograph showing scleral invasion (block arrow) with estrascleral invsion (asterisk) (H&E. original magnification 100×). (C) Optic nerve section showing malignant round blue cells invasion beyond lamina cribrosa (arrow).

Systemic cancer

It is now recognized that a child with retinoblastoma has approximately a 5% chance of developing another malignancy during the first 10 years of follow-up, 18% during the first 20 years, and goes up to 44% at age 45 years.^36,37 The 30-year cumulative incidence is approximately 35% or even higher for those patients who received radiation therapy (external beam therapy) compared with an incidence rate of 6% for those patients who avoided radiation. Osteogenic sarcoma, often involving the femur, is the most common, but other tumors such as spindle cell sarcoma, chondrosarcoma, rhabdomyosarcoma, neuroblastoma, glioma, leukemia, sebaceous cell carcinoma, squamous cell carcinoma, and malignant melanoma have also been recognized as well as brain cancer.³⁷ The mean latency period for the appearance of the second primary is approximately 13 years. Patients who survive a second tumor are at risk for a third, fourth, and even fifth nonocular tumor.³⁸ Carriers of mutant or deleted RB1 who did not receive high-dose radiotherapy have a much higher lifetime risk of common epithelial cancers, particularly cancers of the lung, bladder and, probably, breast, than of sarcomas and other early-onset cancer. Most of the excess cancer risks in hereditary retinoblastoma survivors may be preventable by limiting exposures to DNA damaging agents (radiotherapy, tobacco, and UV light).³⁹ Regarding association of chemotherapy with development of second cancer, Gombos et al.,⁴⁰ reported in their retrospective study that there was a high incidence of secondary acute myelogenous leukemia in retinoblastoma patients after chemotherapy with topoisomerase II inhibitors (etoposide), where 12 out of 15 cases of their cohort had received topoisomerase II inhibitors.

Diagnosis of retinoblastoma

Diagnosis of retinoblastoma depends on the stage of disease presentation. Small intraretinal tumors manifest as innocuous grayish white or translucent lesions in the neurosensory retina. With increase in size, fluid starts to accumulate around the tumor as exudative retinal detachment and the tumor acquire an enlarging caliper feeder artery and draining vein. The tumor shows intra-lesional calcification in 80–90% of cases. Retinoblastoma tumors can grow towards the vitreous cavity and is known as endophytic tumor, where due to discohesiveness of the tumor cells, it easily spread in the vitreous cavity and anterior chamber. Otherwise, the tumor may grow towards the RPE into the subretinal space and is known as exophytic tumor inducing an exudative retinal detachment and pushing the retina anteriorly in the vitreous cavity. Other growth patterns include a diffuse flat infiltration pattern where the retina becomes slightly thickened by presence of tumor cells without any tumefaction pausing a myriad of clinical dilemma in diagnosis like uveitis or pseudohypopyon. Less frequently, the presenting feature can be, hyphema, secondary to iris neovascularization, vitreous hemorrhage, or signs of orbital cellulitis.¹

Differential diagnosis

There is a long listing of differential diagnosis of retinoblastoma. In an oncology referral practice, 48% of lesions referred to as retinoblastoma proved to be pseudoretinoblastoma.⁴¹ Table 3 shows the most common simulating lesions with their differentiating points.¹

Table 3.

Common disease in the differential diagnosis of retinoblastoma.

Lesion	Unilateral	Bilateral	Age	Comments
Retinoblastoma	Yes	Yes	18 mo	Calcium on ultrasound
Toxocariasis	Yes	No	6–11 yr	CT contact with puppies Negative ELISA excludes
PHPV	Yes	No	At birth	Eye typically microphthalmic with inward-drawn ciliary processes, iris Shunt vessels
Coats’ disease	Yes	RARE	18 MO-18 YR	21Ys male, ST quadrant (End 1st decade) leaky telangiectatic RD Vessels. Exudative with lipid. Massive exudation.
ROP	No	Yes	In infancy, but Oxygen not congenital	RX
Retinal dysplasia	--	Yes	Congenital	Microphthalmia, most 13 trisomy
Incontinentia Pigmenti		Yes	Infancy	Bullous skin eruptions, pigmentation
Retinal				Vascular abnormalities, dental and CNS abnormalities, X-linked dominant (lethal in males) 20 retinal detachment
Norrie’s disease	--	X	Congenital	Males, X-linked recessive, Deafness, mental retardation Norrin (gene product)
Medulloepithelioma	X	--	4 yrs	“Diktyoma”, benign and malignant, Teratoid and nonteratoid. Teratoid tumors, contain cartilage, muscle, brain, most ciliary body

Investigations

Once the diagnosis is established, the patient may undergo ultrasonography showing tumor size and intrinsic calcification, Retcam fundus picture, fluorescein angiography (early vascularity and late hyperfluorescence of the tumor), detailed fundus drawings, laboratory work, and an audiogram to check the general status of the patient and effects of systemic chemotherapy when instated. MRI scans is ordered to delineate the extent of intraocular spread, optic nerve and scleral/orbital invasion and to exclude pineal gland tumors. It is contraindicated to perform fine needle aspiration biopsy or open vitrectomy in any suspected retinoblastoma case as this will result in extraocular tumor dissemination. Repeated CT scans are better avoided in bilateral cases as it exposes the body to a radiation dose.

Staging of retinoblastoma

Several classifications of retinoblastoma have been developed to assist in prediction of globe salvage. The most popular grouping is the Reese-Ellsworth classification which classified eyes according to quantity and location of the tumor(s) and its associated features such as vitreous seeding. Their goal was to create a method of predicting success of external beam radiotherapy for retinoblastoma.⁴² Similarly, the International Intraocular Retinoblastoma Classification (IIRC) was created to assess outcomes in standardized protocols of chemotherapy with focal consolidation therapy for retinoblastoma. Those involved in drafting the IIRC reached scientific consensus at the 2003 International Retinoblastoma Symposium in Paris (Table 4).⁴³ A new system of classification for retinoblastoma has recently been introduced by the American Committee on Cancer (2009) using the TNM system to classify the tumor7. This classification system describes both clinical (c-TNM) and pathological (p-TNM) classifications and accounts for both intraocular and extraocular disease. Adopting the TNM classification system would allow for the proper interpretation of results of future clinical trials. It is vital that the classification be instituted exactly as intended, and its use is now mandatory when publishing in important peer-reviewed journals (Table 5).⁴⁴

Table 4.

International retinoblastoma symposium (Paris, 2003).

Group A

All tumors are 3 mm or smaller, confined to the retina and at least 3 mm from the foveola and 1.5 mm from the optic nerve. No vitreous or subretinal seeding is allowed

Group B

Eyes with no vitreous or subretinal seeding and discrete retinal tumor of any size or location. Retinal tumors may be of any size or location not in group A. Small cuff of subretinal fluid extending ⩽5 mm from the base of the tumor is allowed

Group C

Eyes with focal vitreous or subretinal seeding and discrete retinal tumors of any size and location. Any seeding must be local, fine, and limited so as to be theoretically treatable with a radioactive plaque. Up to one quadrant of subretinal fluid may be present

Group D

Eyes with diffuse vitreous or subretinal seeding and/or massive, nondiscrete endophytic or exophytic disease. Eyes with more extensive seeding than Group C. Massive and/or diffuse intraocular disseminated disease may consist of ‘greasy’ vitreous seeding or avascular masses. Subretinal seeding may be plaque-like, includes exophytic disease and >1 quadrant of retinal detachment

Group E

Eyes that have been destroyed anatomically or functionally with one or more of the following: Irreversible neovascular glaucoma, massive intraocular hemorrhage, aseptic orbital cellulitis, tumor anterior to anterior vitreous face, tumor touching the lens, diffuse infiltrating retinoblastoma, phthisis or pre-phthisis

Table 5.

Definitions of tumor, node and metastasis.

Clinical classification (cTNM)

Primary tumor (T)

TX Primary tumor cannot be assessed

T0 No evidence of primary tumor

T1 Tumors no more than 2/3 the volume of the eye with no vitreous or subretinal seeding

• T1a: No tumor in either eye is greater than 3 mm inlargest dimension or located closer than 1.5 mm to the optic nerve or fovea (coinciding with IIRC Group A)

• T1b: At least one tumor is greater than 3 mm in largest dimension or located closer than 1.5 mm to the optic nerve or fovea. No retinal detachment or subretinal fluid beyond 5 mm from the base of the tumor (coinciding with IIRC Group B)

• T1c: At least one tumor is greater than 3 mm in largest dimension or located closer than 1.5 mm to the optic nerve or fovea, with retinal detachment or subretinal fluid beyond 5 mm from the base of the tumor (coinciding with IIRC Group C)

T2 Tumors no more than 2/3 the volume of the eye with vitreous or subretinal seeding

Can have retinal detachment

• T2a: Focal vitreous and/or subretinal seeding of fine aggregates of tumor cells is present, but no large clumps or “snowballs” of tumor cells (coinciding with IIRC Group C)

• T2b: Massive vitreous and/or subretinal seeding is present, defined as diffuse clumps or “snowballs”of tumor cells (coinciding with IIRC Group D)

T3 Severe intraocular disease

• T3a: Tumor fills more than 2/3 of the eye(coinciding with IIRC Group D)

• T3b: One or more complications present, which mayinclude tumor-associated neovascular or angle closure glaucoma, tumor extension into the anterior segment, hyphema, vitreous hemorrhage, or orbital cellulitis (coinciding with IIRC Group E)

T4 Extraocular disease (detected by imaging studies)

• T4a: Invasion of optic nerve

• T4b: Invasion into the orbit

• T4c: Intracranial extension not past chiasm

• T4d: Intracranial extension past chiasm

Regional lymph nodes (N)

NX: Regional lymph nodes cannot be assessed

N0: No regional lymph node involvement

N1: Regional lymph node involvement (preauricular, cervical, submandibular)

N2: Distant lymph node involvement

Metastasis (M)

M0 No metastasis

M1 Systemic metastasis

• M1a: Single lesion to sites other than CNS

• M1b: Multiple lesions to sites other than CNS

• M1c: Prechiasmatic CNS lesion(s)

• M1d: Postchiasmatic CNS lesion(s)

• M1e: Leptomeningeal and/or CSF involvement

Management of retinoblastoma

Priorities in management of intraocular retinoblastoma are tumor control. By controlling the tumor, the ophthalmic oncologist saves human life. Of course, the optimum method for tumor control is to save the eye and vision. Unfortunately, with advanced disease, the eye has to be sacrificed by enucleation. This should be carried out with no hesitation in order to save human life.

The therapeutic approach depends on staging of the disease, laterality, systemic status, metastatic potential, and risk of second cancer. Treatment is usually prolonged over many months requiring repeated visits for active management and lifelong follow up. In our area of the world, the socioeconomic status of the patient has to be considered in decision making and its ability to commit. If the decision comes to enucleation, it is important to spend time explaining to the parents the necessity and the drawbacks of delaying the decision on the life of the child and to answer every question in the mind of the parents about cosmetic rehabilitation of the child.

Currently available treatment methods for retinoblastoma include intravenous chemoreduction, diode laser thermotherapy, cryotherapy, plaque radiotherapy, external beam radiotherapy, enucleation, orbital exenteration, and systemic chemotherapy for metastatic disease.⁴⁴ Unilateral retinoblastoma usually present at a late stage and are generally managed with enucleation if the eye is classified as stage E; for those eyes in groups A to D, chemoreduction or focal measures are used. For bilateral retinoblastoma, chemoreduction is utilized in most cases even if one eye is harboring an advanced disease. Enucleation decision is delayed till the end of six cycles and active focal management of the more advanced eye is usually carried out after the second cycle of chemotherapy, along with focal treatment of the less advanced eye.

Chemoreduction

Systemic chemoreduction is given to the patients in order to reduce tumor volume to allow for therapeutic measures to be more focused, effective and affecting less of the retinal tissues not harboring tumor anymore.46 Systemic chemotherapy regimen for chemoreduction of retinoblastoma is not uniformly agreed upon. One,^47,48 two,⁴⁹ three,^50–53 and even four⁵⁴ drug regimen have been used with almost similar results in tumor control and ocular salvage. There is a general consensus about the use of systemic chemotherapy for six cycles given every 3–4 weeks. Two-drug regimen of systemic chemotherapy using carboplatin and etoposide were found to have mild and reversible acute side effects in our study.³ The toxicity of vincristine reported to be in up to 40% of patients was avoided using this protocol.⁵⁵ We use systemic chemotherapy regimen for six cycles given every 3–4 weeks to allow for adequate tumor reduction. Following two cycles of systemic chemotherapy, most tumors shrink with a mean of 35% in tumor base and 50% in thickness with resolution of subretinal fluid. Focal therapy to the individual tumors is usually delivered at cycle 2. With such a regimen, tumor control was achieved in 100% of group A eyes, 93% of group B eyes, 86% of group C eyes, 48.8% of group D eyes and 0% for group E eyes. Our results for globe survival matched the reported literature in developing countries^53,56,57 and approaching results of developed countries.^{49–52,54,55}

After finishing active management, follow up is warranted. The child is examined under anesthesia monthly to observe for new tumor development, marginal recurrence or seeds reactivation following the disappearance of the tumor inhibiting effect of chemotherapy. Focal therapy is delivered according to the situation, and the follow up is kept monthly as long as active management is performed. Recurrent tumors, new tumors or retinal seeds recur in the first 2 years after treatment and it is crucial to early detect and properly manage recurrences.^58,59

Focal therapies

Focal therapies include transpupillary diode laser thermotherapy (TTT), cryotherapy, and plaque radiotherapy. Commonly, focal therapies are applied to an eye while the child is receiving chemoreduction, and they are repeated to each tumor at each chemotherapy session. We insist on delivering focal therapy the same day or the day before chemotherapy to enhance the synergistic effect of thermotherapy to chemotherapy.⁵⁹

The goal is to deliver a temperature of 42–60 °C, a temperature that is below the coagulative threshold and thus sparing the retinal vessels of photocoagulation. The combination of heat and chemotherapy is termed chemothermotherapy. Power settings depend on the tumor thickness with thinner tumor receiving less power. Usual range of power settings with diode laser TTT is from 300 to 800 mW applied to cover the whole tumor surface with a safety margin around it. Usual set up of the laser machine is 10 min and the large spot laser indirect ophthalmoscope is applied over the lesion for sometime and moved slowly to cover the tumor aiming at seeing a delayed onset grayish white reaction, thus ensuring significant in-depth tumor penetration. It is important to spend time treating tumors with subtle dispersed retinal seeds (Fig. 4B).

Plaque radiotherapy is used as a primary or more commonly a secondary treatment modality for tumors that fail other focal therapies, even those that reach a moderate size, up to 8 or 10 mm in thickness. We use Ruthenium/Rhodium-106 applicators which are mainly emitting Beta irradiation up to a tumor thickness of 6–7 mm after placing the plaque over the sclera to cover the tumor base with an extra 2–3 mm of safety margin. Different plaque diameters exist up to 25 mm wide. The radiation dose to the tumor apex is around 50 Gy delivered over a period of 2–5 days depending on plaque activity. Tumor control rate following plaque radiotherapy as a primary therapy or after failed chemothermotherapy is about 90%. Success decreases to 75% if plaque is used after tumor recurrence following external beam radiotherapy and mounts to 75% (Fig. 4 D).⁶⁰

Cryotherapy is applied for peripheral tumors under 3 mm in greatest dimension. A triple freeze thaw application is used insisting on seeing the ice ball beyond the apex of the tumor at each application. It is a critical modality for management of recurrent subretinal seeds near the ora serrata.

External beam radiotherapy

This modality uses photons delivered from a remote machine to the eye. EBRT has fallen out of use because of its local complications effect and associated high incidence of second cancers in the irradiated zone years after cure from the disease in hereditary forms of retinoblastoma. EBRT is preserved only to bilateral advanced disease with diffuse vitreous seeds as a last globe preserving modality in patients refusing bilateral enucleation after failure of all other conservative treatment modalities. We should specify to radiologist to give a “whole eye technique” to cover the diffuse vitreous seeds when radiotherapy is required. A “lens sparing technique” might give adequate control if combined with focal therapy to cover the peripheral tumors at the ora serrata.⁶¹ External beam radiotherapy may induce a second cancer in the field of irradiation, and this was the driving force behind the use of systemic chemotherapy for chemoreduction that is largely replaced external beam radiotherapy.^36–38,62

Subconjunctival chemoreduction for retinoblastoma

Increasing interest has emerged in delivering chemotherapy locally to the eye while minimizing systemic exposure. Chemotherapy has been given as posterior subtenon carboplatin injection (20 mg/2 cc)⁶³ or carboplatin given as a nanomolecule.⁶⁴ Periocular topotecan is injected in a fibrin sealant⁶⁵ or as an episcleral implant.⁶⁶ Other delivery systems included depot gels,solid polymers, miniature catheters placed adjacent to the sclera and iontophoresis systems.⁶⁷ Local side effects include inflammation, ptosis, scarring and loss of sight.⁶⁷

Posterior subtenon periocular boost of subconjunctival chemotherapy is given in advanced retinoblastoma in both eyes or in their only remaining eye along with systemic chemoreduction.

Selective intraophthlamic artery melfalan injection

Japanese investigators have been using an interventional radiology technique of infusing melfalan into the carotid artery for retinoblastoma since 1988. Their technique used a balloon catheter inserted into a femoral artery puncture and a (balloon) catheter that was passed into the internal carotid artery and inflated to occlude the internal carotid artery (for as long as 30 min) beyond the orifice of the ophthalmic artery, allowing chemotherapy infused into the cervical internal carotid artery to perfuse the eye selectively without perfusing the brain. In 1452 procedures of 1469 trials, the eye preservation rate was 100% in group A, 88% in group B, 65% in group C, 45% in group D, and 30% in group E according to the International Classification of Intraocular Retinoblastoma. Two eyes (0.5%) developed severe orbital inflammation, and 2 eyes (0.5%) had diffuse chorioretinal atrophy. Transient periocular swelling or redness occurred in some cases. No severe systemic adverse events were detected. Transient bronchospasm occurred in 1 patient (0.3%), and transient vomiting occurred in several patients.⁶⁸

In 2008, Abramson et al., reported preliminary results of a modified technique by directly injecting melfalan into the ophthalmic artery using a microcatheter. The goal was to achieve a targeted focal delivery of chemotherapy to the tumor with minimal systemic complications and possibly more efficacy. Since then, the technique has been adopted in many centers worldwide.^69–71

Superselective ophthalmic artery infusion of chemotherapy was used initially as an ocular salvage therapy in advanced group V retinoblastoma as a primary and secondary treatment modality. With more comfort of the technique, cannulation of one or both ophthalmic arteries with chemotherapy injection could be done via femoral artery cannulation and is used in less advanced disease stage as a primary or secondary treatment modality. This technique seems to control advanced disease, subretinal seeds and vitreous seeds whether primary or recurrent (Fig. 6).^72,73

Figure 6.

(A) Vitreous seeds and inferonasal tumor recurrence following chemofocal therapy and external beam radiation for unilateral sporadic retinoblastoma. (B) Tumor and vitreous seeds control following 3 monthly injection of intraophhtlamic artery melfalan.

A recent report showed that the globe salvage rate in group E in eyes managed with intra-arterial chemotherapy was 30%. Three injections at monthly intervals were given and subretinal and vitreous seeds recurrence was noted at one year follow up necessitating enucleation.⁷⁴

The minimum age with successful cannulation was 3 months and the main drug used is melfalan, at a dose of (0.35 mg/kg) or 5–7.5 mg/injection. Other additional drugs include topotecan and carboplatin depending on the stage of the disease and tumor response.⁶⁹

Reported complications include transient eyelid edema, blepharoptosis, cilia loss, and orbital congestion with temporary dysmotility. Vascular events are of concern and include ophthalmic artery stenosis (permanent or temporary). Concomitant central or branch retinal artery occlusion (permanent or temporary). Retinal pigment epithelial mottling with development of later-onset underlying choroidal atrophy. Sectoral choroidal occlusive vasculopathy leading to chorioretinal atrophy was also observed (Fig. 7). There was no evidence of metastasis, stroke, brain injury, or persistent systemic toxic effects.^75,76

Figure 7.

Ophthalmic artery occlusion with severe choroidal RPE mottling following a second injection of ophthlamic artery melfalan.

In a study of enucleated globes following intraarterial melfalan, showed a range of tumor response from complete regression to no regression with viable tumor. Ischemic atrophy involving the outer retina and choroid was noted, with foreign intravascular foreign material resembling granulomatous reaction observed within occluded vessels.⁷⁷

Selective ophthalmic artery melfalan injection is a promising new technique. We have been using this technique to treat 20 patients with advanced stage D/E disease in addition to focal therapy (Othman et al., unpublished data). Two of the patients experienced ophthalmic artery occlusion (Fig. 7). Eleven of 15 cases of stage E disease and 2 out of 5 cases of stage D ended up by enucleation. All cases were combined by focal therapy. It is our recommendation to cautiously use this technique for advanced disease as a last resort of therapy when the patient’s family is refusing enucleation as a primary and/or secondary ocular salvage procedure.

Enucleation

Enucleation is an important tool in management of retinoblastoma. It is indicated in advanced unilateral disease, stage E retinoblastoma, after failure of tumor control by other modalities, or in eyes with secondary glaucoma, vitreous hemorrhage, hyphema, pseudohypopyon. Enucleation is associated with placement of an orbital implant of adequate size made of porous implants (hydroxyapatite, porous polyethylene, or aluminium oxide) or non-porous implants like polymethylmethacrylate sphere and silicone, wrapped in donor sclera, or synthetic viryl mesh or directly placed in the orbit with attachment of the 4 recti muscles around it using 6/0 Vicryl sutures.⁷⁸ Closure of conjunctiva should be in layers starting by the tenon’s capsule then the conjunctival layer. The superior rectus muscle should not be tightened to the muscle complex to avoid induced ptosis by pulling on the rectus/levator complex and adding to the superior margin of the prosthesis, to restore functional length and create a more anatomic pivot point for the levator muscle.⁷⁹ It is important to check the integrity of the fornices and to put a conformer at the end of surgery. Handling the globe should be done according to the following guidelines.

Advanced stage E unilateral disease is managed by enucleation as it is more likely to have elevated intraocular pressure, invasion of the anterior chamber, uveal tract, optic nerve and sclera on histopathological examination.⁸⁰

In unilateral retinoblastoma, about 70% of cases are managed by enucleation due to late presentation. Our philosophy in management of bilateral cases was to initiate systemic chemoreduction using carboplatin and etoposide for six cycles, start to manage both eyes with focal therapy mainly from the second chemotherapy cycle, delaying the decision for enucleation of the advanced eye till the end of chemotherapy to assess the response and to perform enucleation when indicated using the largest possible orbital implant in a more suitable environment for surgery. This practice might be associated with less orbital volume growth retardation through delaying enucleation beyond the first year of life.^81,82

We agree with others regarding the importance of adequate orbital volume replacement in pediatric population to obviate the need of further surgeries in adulthood.⁸² As a rule of thumb, we use an 18 mm diameter orbital implant before 1 year of age and a 20 mm orbital implant after 1 year of age in orbital volume replacement. An 18 mm implant has a volume of 3.1 ml and a 20 mm implant replaces an orbital volume of 4.2 ml.⁸³ An enucleated globe has a volume of 5.5–9 ml depending on age and globe size.⁸⁴ Both silicone implant and hydroxyapatite implants are used in our practice. There was no tumor progression under chemotherapy in our series even in eyes with advanced disease. A recent report indicated significant orbital growth retardation after enucleation, even with a hydroxyapatite implant. Orbital growth retardation was correlated with operation age and also more prominent in children treated in the first year of life.⁸²

Pathologic staging

If an eye is enucleated, pathology could provide histologic verification of the disease and pathologic staging could provide information complementary to the clinical staging. Both clinical and pathologic data may be used to plan the management of a case. The International Retinoblastoma Staging Working Group (IRSWG) uniformed definitions of the pathological entities: massive choroidal invasion stated as a maximum diameter (thickness or width) of invasive tumor focus of 3 mm or more that may reach the scleral tissue. Focal choroidal invasion is defined as a tumor focus of less than 3 mm (thickness or width) and not reaching the sclera. Optic nerve invasion is classified as prelaminar, laminar, retrolaminar, or tumor at surgical margin, and the measurement of the depth of invasion should also be recorded.

Handling of the enucleated globe

When fresh tumor is required, it is important that the enucleated globe be moved to a sterile area in the operating room away from the operative field due to the risk of contaminating the operating field with the harvested tumor cells. After collecting the specimen, the surgeon should change his/her gloves before re-entering the operative field. The optic nerve should be measured for length and the cut margin should be obtained before opening the eye. The first technique proposed is the opening of a window in the sclera at the edge of the area containing most of the tumor. The window may be obtained using a corneal trephine or by using a sharp blade. Fresh tumor then should be retrieved from areas without necrosis. After tumor harvesting, the eye is then placed in sufficient formalin to cover the globe and fixed for at least 48 h.

Consensus was reached as to the examination of the entire eye microscopically by submitting a total of four blocks. One block is the central pupil–optic nerve (PO) section containing the optic nerve, tumor, and anterior chamber structures. Two blocks will contain the calottes (remainder of ocular tissue after obtaining the PO) in anterior–posterior segments embedded on edge to examine more choroidal surface. The fourth block contains the cross section of the margin of the optic nerve, obtained before opening the eye. The slides of the PO section should contain the optic nerve head, lamina cribrosa, and postlaminar optic nerve in a single plane of section.⁸⁵

Table 6 demonstrates histopathologic classification of enucleated globes.

Table 6.

Pathologic classification (pTNM).

Primary tumor (pT)

pTX Primary tumor cannot be assessed

pT0 No evidence of primary tumor

pT1 Tumor confined to eye with no optic nerve or choroidal invasion

pT2 Tumor with minimal optic nerve and/or choroidal invasion:

• pT2a: Tumor superficially invades optic nerve head but does not extend past lamina cribrosa or tumor exhibits focal choroidal invasion

• pT2b: Tumor superficially invades optic nerve head butdoes not extend past lamina cribrosa and exhibits focal choroidal invasion

pT3 Tumor with significant optic nerve and/or choroidal invasion:

• pT3a: Tumor invades optic nerve past lamina cribrosa but not to surgical resection line or tumor exhibits massive choroidal invasion

• pT3b: Tumor invades optic nerve past lamina cribrosa but not to surgical resection line and exhibits massive choroidal invasion

pT4 Tumor invades optic nerve to resection line or exhibits extraocular extension

elsewhere

• pT4a: Tumor invades optic nerve to resection line but no extraocular extension identified

• pT4b: Tumor invades optic nerve to resection line and extraocular extension identified

Regional Lymph Nodes (pN)

pNX Regional lymph nodes cannot be assessed

pN0 No regional lymph node involvement

pN1 Regional lymph node involvement (preauricular, cervical)

pN2 Distant lymph node involvement

Metastasis (pM)

cM0 No metastasis

pM1 Metastasis to sites other than CNS

• pM1a Single lesion

• pM1b Multiple lesions

• pM1c CNS metastasis

• pM1d Discrete mass(es) without leptomeningeal and/or CSF involvement

• pM1e Leptomeningeal and/or CSF involvement