Tumor Syndromes Predisposing to Osteosarcoma

Abstract

Osteosarcoma is the most common primary bone tumor affecting predominantly adolescents and young adults. It accounts for about 5% of all childhood cancers. While the majority of osteosarcomas are sporadic, a small percentage occur as a component of hereditary cancer syndromes. Early onset, bilateral, multifocal and metachronous tumors suggest genetic predisposition. The inheritance patterns can be autosomal dominant or recessive. These syndromes predispose to a wide variety of mesenchymal and epithelial cancers with propensity for certain mutations being prevalent in specific cancer subtypes. Li-Fraumeni syndrome (LFS), Retinoblastoma (RB), Rothmund-Thompson syndrome (RTS Type 2), Werner Syndrome (WS) and Bloom syndrome (BLM), constitute the majority of the tumor syndromes predisposing to osteosarcoma and will be the focus for this review.

Introduction

Osteosarcoma (OS) accounts for 1% of all cancer cases in the United States with a bimodal peak of incidence, one occurring in adolescents and the other in the elderly¹. The majority of the tumors are high grade and as the name implies, production of neoplastic immature osteoid is the “sine qua non” for diagnosis of this malignancy². Prognosis of conventional high grade osteosarcoma without clinically detectable metastases is 70-80% 5-year survival with standard chemotherapy, and drops to 20-40% for those who present with metastatic disease^3,4. Unlike other childhood sarcomas such as Ewing sarcoma, which are characterized by simple chromosomal rearrangements and low mutation rates, osteosarcoma is a genetically diverse disease with chromosomal copy number changes, structural rearrangements, and mutations⁵.While genomic screening over decades with multiple advancing technologies has not pinned down the etiology of osteosarcoma, a higher incidence of OS relative to general population has been consistently found in some cancer predisposition syndromes. These syndromes include Li-Fraumeni Syndrome (TP53), Retinoblastoma (RB1), Rothmund-Thompson Syndrome (RECQL4), Bloom (BLM) and Werner Syndromes (WRN) with individuals inheriting germline inactivating mutations of the respective genes^6–10. The expression of disease, mutation spectrum and age of onset can vary even within family and the pattern of inheritance can be autosomal dominant or recessive¹¹ (Table 1).

Table 1:

Osteosarcoma Predisposition Syndromes

Predisposition Syndrome	Inheritance Pattern	Gene	Chromosome	Tumor Types
Li-Fraumeni	AD	TP53	17p13.1	Osteosarcoma, Soft Tissue sarcoma, Breast Cancer, Leukemia, Adrenocortical Carcinoma, Brain Tumors
Retinoblastoma	AD	RB1	13q14.2	Osteosarcoma, soft tissue sarcoma, melanoma
Rothmund Thompson	AR	RECQL4	8q24.3	Osteosarcoma, squamous and basal cell carcinoma
Werner	AR	WRN	8p12	Osteosarcoma, soft tissue sarcoma, Melanoma, Myeloid, Thyroid cancer, other epithelial cancers
Bloom	AR	BLM	15q26.1	Carcinomas, Lymphomas, leukemias, osteosarcoma

AD:Autosomal Dominant; AR:Autosomal Recessive

Osteosarcoma Predisposing Syndromes:

Hereditary Retinoblastoma:

Hereditary retinoblastoma (OMIM# 180200) is a rare autosomal dominant disorder of infancy caused by biallelic mutation of the RB1 gene in developing retinal tissue. Inherited mutation of RB1 in one allele is a predisposing factor for the development of retinoblastoma following the mutation of the second allele^12,13. In 1971, Dr. Alfred G. Knudson proposed his “two-hit” hypothesis stating that Retinoblastoma is a cancer caused by two mutational events based on his review of 48 hereditary and sporadic cases between 1944-1969 at M.D Anderson Hospital¹⁴. He proposed that in the inherited form, one mutation is inherited via germ cells and the second one occur in somatic cells, and in the sporadic form both mutations occur in somatic cells (Fig 1). The break-through and genetic proof of his hypothesis came to fruition by the discovery of a missing 13q DNA clone sequence in a Retinoblastoma patient which was later shown to be possess conserved RB1 sequence^15–18. Retinoblastoma has an incidence of about 1 in 18000 live births and affects all races throughout the world¹⁹. The RB1 gene has 27 exons and encodes a 928 amino acid Rb protein (pRb). These are composed of two pocket proteins (p107) and (p130) which regulate cell cycle by binding to E2F family of transcription factors^20–22. Over 1000 different RB germline and somatic mutations have been reported worldwide and the mutations are distributed throughout the gene. Several recurrent and hot spot mutations have been reported and the spectrum of mutations include deletions, nonsense mutations, missense mutations, indels, promoter, splicing mutations and also epigenetic changes such as promoter methylation ^23–26 (Fig 2A). In a study by Dommering et al, in a comprehensive cohort of 500 Dutch Rb patients from the Dutch Retinoblastoma Register, more than 180 Rb mutations were found including 33 novel mutations²⁷. Mutations included nonsense, frame shift, missense, splice site, large indels, chromosomal deletions and promoter hypermethylation. This study found that the distribution of mutations in this cohort did not differ from that described in worldwide distribution²³. In the searchable database (RBGMdb) which is based on 932 publications²³ deletions and nonsense mutations were found to be the main inactivating events and nearly 40% of the mutations were recurrent and localize to 16 hot spots with predominance of C to T conversions and the reminder of mutations were scattered along the gene. Genotype-phenotype correlations, mechanisms linking mutations to ethnicity, delayed onset and low penetrance could be ascertained from this study. The contribution of mutation types to secondary malignancies is not well known.

Fig 1:

Schematic Diagram of “Two-Hit” Hypothesis- One mutation is inherited through germline followed by second mutation or mitotic recombination in somatic cells

Fig 2 A and B:

A. Plain radiograph showing mixed lytic and sclerotic lesion in distal femoral metadiaphysis with multiple soft tissue calcifications (arrows). B. MR TW and T2W FS images showing distal femoral marrow lesion with a large soft tissue mass (Courtesy: Dr. Sinchun Hwang-MSKCC)

Some patients with sporadic retinoblastoma cases may carry a mosaic RB1 mutation²⁸, and detecting these low-level variants is important for screening and for family planning purposes. Additionally, individuals who present with retinoblastoma and a detected pathogenic RB1 germline variant may either be a “de novo” case, or one parent may be a germline mosaic for the variant. In the latter case, there is a substantial risk of other children of this parent developing retinoblastoma.

Osteosarcoma Association:

While the children with hereditary retinoblastoma have excellent survival, they are at increased risk for developing bone and soft tissue sarcomas, most notably osteosarcoma^29,30. This risk is attributed to genetic factors, radiation therapy and chemotherapy, with radiation therapy carrying the highest risk^30–33. While a 69-fold increase in the development of osteosarcoma has been reported, this can dramatically rise to 400-fold after radiation exposure, compared to population rates³². The age incidence is similar to sporadic osteosarcoma (adolescents and young adults) and the most common site of location is within the radiation field, however tumors also occur outside the radiation field such as lower extremities^30,31,34,35. Kleinerman RA et al reported the location of osteosarcomas included skull and face (61%), lower limbs (29%), trunk (7%) and unknown locations (3.8%) in 75 patients with hereditary retinoblastoma following radiation³⁰. In a retrospective review of skull-based malignancies in hereditary retinoblastoma survivors at Memorial Sloan Kettering Cancer Center, osteosarcomas accounted for 39% of the tumors³⁶. The incidence of somatic RB1 mutation in sporadic osteosarcoma ranges between 30-75% ³⁷.

Imaging and Pathology: Radiological findings are similar to conventional sporadic osteosarcoma. Lesions are destructive, ill defined, mixed lytic and sclerotic with wide transition zone and extend beyond cortex with soft tissue mass and calcifications (Fig 2). Pathological features are often typical with production of neoplastic osteoid and morphology showing osteoblastic, chondroblastic, MFH-like or telangiectatic features (Fig 3).

Fig 3 A and B:

A. Photomicrograph of osteosarcoma showing broad islands of osteoid matrix surrounded by tumor cells with an adjacent chondroid component (200X). B. High power view of osteoid matrix showing irregular mineralization surrounded by osteoblasts and pleomorphic tumor cells (400X)

Li-Fraumeni Syndrome (LFS)

Described in 1969 by Drs. Frederick Li and Joseph F. Fraumeni Jr, this hereditary cancer predisposition syndrome is associated with sarcomas, breast carcinoma, brain tumors, leukemias and adrenocortical carcinomas². LFS (OMIM #151623) is an autosomal dominant disorder and is characterized by germline mutations in TP53 gene^3,4. Classic Li-Fraumeni criteria include proband diagnosed with sarcoma before age 45, has first –degree relative with any cancer before age 45 and another first or second degree relative with any cancer before age 45 or sarcoma at any age². LFS is associated with an extremely high lifetime risk of cancer. The risk of cancer has been estimated to be 50% by 30 years of age and 90% by age 60 years ³⁸, and the relative risk of osteosarcoma has been estimated at 107 ³⁹. Pathogenic germline variants in TP53 result in protein loss of function. While nonsense, frameshift and splicing variants can span the gene sequence, many of the pathogenic missense variants in TP53 occur within the DNA binding domain (DBD)^5,6

LFS has been detected in approximately 5% of osteosarcoma cases under the age of 30, and osteosarcoma is the most common sarcoma found in individuals with LFS ⁷. The same study found no cases of Li-Fraumeni syndrome in osteosarcoma patients with onset >30 years of age ⁷. Moreover, osteosarcoma is diagnosed in approximately 12% of individuals with LFS ⁴⁰. Since osteosarcoma is relatively common in LFS families and the age of onset is early, it may be the first presenting neoplasm in a family suggestive of LFS. For example, the family presented in figure 4 was brought to clinical attention when the proband was diagnosed with osteosarcoma at age 19. His 56 year old father was then diagnosed with leiomyosarcoma, melanoma, and an adrenocortical neoplasm and both tested positive for Li Fraumeni syndrome. Other than a typically younger age of onset, the presentation of osteosarcoma in LFS patients is similar to sporadic osteosarcoma with metaphysis of long bones as the most commonly affected site ⁸. Histological features are similar to conventional osteosarcomas and the tumor is composed of pleomorphic tumor cells containing variable amounts of osteoid matrix and can be sub-typed as osteoblastic, chondroblastic and fibroblastic types depending on the predominant matrix produced by the tumor ²

Fig 4 A-D:

A. Pedigree of LFS family. B. Plain radiograph showing a large densely calcified mass in right iliac bone and acetabulum with extraosseous mass and poorly defined periosteal reaction (arrow) Coronal CT scan Coronal CT shows a right iliac lesion with mixed lytic and sclerotic components extending to the right ilium and acetabulum with extensive periosteal reaction (arrows) (Courtesy: Dr.Sinchun Hwang-MSKCC). C. Photomicrograph of the tumor showing lace –like pink osteoid surrounded by osteoblastic tumor cells (400X). D. Next generation sequencing analysis of DNA extracted from tumor and peripheral blood of proband -IGV genome browser screenshot showing a TP53 c.916 C>T (p.Arg306*)exon 8 mutation seen in both tumor sample and normal (peripheral blood).

Families with LFS often show genetic anticipation, with earlier onset of cancers in successive generations. This phenomenon may be attributed to telomere shortening^41,42. The most common TP53 mutations in sarcoma patients of LFS are missense mutations (72.8%) and involve codons 273,248,282,175 and 220 in the DNA binding domain (DBD)⁸. High prevalence of codon 245 and 282 were seen in osteosarcoma whereas more than 20% of all mutations are seen at codon 273 in patients with rhabdomyosarcoma⁸. Mutations outside the DBD (codons 337 or 344) are associated with leiomyosarcoma and unlike osteosarcoma and rhabdomyosarcoma, frameshift, splice –site and nonsense mutation are more frequent. It is postulated that mutations predicting absence of wild type protein lead to late-onset type sarcoma and missense DBD mutations accumulating mutant proteins give rise to early onset types of sarcoma such as osteosarcoma and rhabdomyosarcoma⁸.For those with a known germline mutation in TP53, recommended screening includes whole body MRI to screen for sarcomas and other cancers ⁴³.

Werner Syndrome:

Werner Syndrome, an autosomal recessive disorder (OMIM#27770), also known as adult progeria is characterized by premature aging, bilateral cataracts, osteoporosis, short –stature and scleroderma –like skin changes⁴⁴. Founder effect contributes to the high frequency seen in Japan⁴⁵. Werner Syndrome is caused by mutations of the WRN gene, which is a RecQ helicase, located on chromosome 8p11.1 ⁴⁶. Patients with Werner Syndrome are susceptible to multiple cancers including osteosarcoma, soft tissue sarcoma, meningioma, myeloid disorders, melanomas, thyroid carcinoma, hematological malignancies and other epithelial cancers⁴⁴. The WRN gene is the only RecQ helicase with a 3’-5’ exonuclease activity. More than 90 mutations have been identified and they are all inactivating and include base substitutions, insertions, deletions and complex mutations, which disrupt the WRN, open reading frame ⁴⁷. WRN gene is composed of 35 exons that encode a 1432 amino acid protein which contains RecQ-type helicase domains in central region and an exonuclease domain in N-terminal region. There are two consensus regions, RecQ helicase conserved region (RQC), the helicase RNaseD C-terminal conserved region (HRDC), which are present between the helicase and nuclear localization signal⁴⁷. Osteosarcomas occur at a later age in these patients (ages ranging from 35-57) and tend to present at atypical sites such as foot, ankle, patella in contrast to more common sites such as long bones⁴⁸. An association of WRN SNP 1367R with bone and soft tissue sarcomas has been reported in Werner Syndrome with R allele having a protective effect⁴⁹.

Rothmund –Thompson Syndrome (RTS)

Rothmund-Thompson syndrome (OMIM #268400) is an autosomal recessive disorder caused by biallelic germline mutations in RECQL4, and is strongly associated with osteosarcoma predisposition²¹. The syndrome usually presents with a characteristic rash in infancy and is also characterized by poikiloderma, sparse hair, frontal bossing, saddle nose, short stature, radial defects, hypoplastic patellae, esophageal or pyloric atresia, annular pancreas, myelodysplasia and cataracts²¹. Pathogenic mutations in RECQL4 are loss of function mutations and include nonsense, frameshift, splice site and intronic deletions²³. Unlike other TP53 and RB mutated syndromes, RECQL4 mutations are not seen in sporadic OS, and present in the context of Rothmund-Thompson syndrome²³. In a review of 61 patients with RTS by Stinco et al²⁴, OS accounted for 62% of cancers, of which 3 were multicentric (metachronous) and 12 developed before the age of ten. Another cohort of 41 RTS patients found that 32% of patients developed osteosarcoma, though 22/41 (54%) of patients in this study were under the age of 15, so the incidence of osteosarcoma in RTS may be higher⁵⁰. An association of gene truncation mutations with development of OS has been proposed by some authors²⁵. Histological subtypes described are similar to conventional OS and multimodality chemotherapy has been recommended as treatment of choice²⁶ based on outcome on a series of 7 patients. A second syndrome caused by RECQL4 mutations and predisposition to OS is RAPADILINO syndrome²¹. The name is the acronym for: RA: Radial dysplasia; PA: Patella aplasia or hypoplasia and left high arched palate; DI: Diarrhea and Dislocated joints; LI: Little size and Limb malformations; NO: long, slender Nose and NOrmal Intelligence)²¹. Most individuals with RAPADILINO syndrome carry a specific founder mutation, RECQL4 c.1390+2delT, and also have an increased risk of osteosarcomas and lymphomas⁵¹.

Bloom Syndrome (BLM):

Bloom Syndrome (OMIM#210900) is an autosomal recessive disease characterized by short stature, sun sensitive rash and sparse subcutaneous fat and is caused by mutations in BLM gene, which is a RecQ helicase⁵². While majority of the cancers in BLM are carcinomas, leukemias and lymphomas, the osteosarcoma rate is higher than general population⁵³. The prevalence rate in Ashkenazi Jews is 1% and susceptible individuals can be offered genetic testing⁵⁴.

Summary

In syndromes predisposing to osteosarcoma, tumor presentation can be the first manifestation and presenting diagnosis. This possibility should be considered especially in cases with unusual presentation and family history of other cancers. The rarity of these syndromes is a challenge and a high index of suspicion is needed to pursue genetic counseling and further testing to detect underlying heritable mutations. Through next generation sequencing technology we have learned that there is a higher than expected prevalence of hereditary cancer predisposition syndromes in advanced cancer patients. In a recent study of 1040 patients with advanced cancers, germline sequencing of a broad panel of cancer related genes showed 17.5% of the individuals had clinically actionable heritable mutations, and over half of these mutations would not have been detected using clinical guidelines alone⁵⁵. In rare cancers such as osteosarcoma which affects young individuals, early recognition of patients with predisposition syndromes allows for genetic testing of at-risk family members, better surveillance and possible targeted treatment options.