The Cutting Edge of Skin Cancer in Transplant Recipients: Scientific Retreat of International Transplant Skin Cancer Collaborative and Skin Cancer in Organ Transplant Patients Europe

Abstract

The International Transplant Skin Cancer Collaborative (ITSCC) is an organization of more than 300 physicians and scientists focused on the study of dermatologic changes following solid organ transplantation. Transplant patients have a 100-fold increased risk of developing skin cancer. In October 2012, ITSCC and its European counterpart Skin Cancer in Organ Transplant Patients Europe held a joint biennial retreat in Essex, MA to discuss novel findings in the pathogenesis and management of skin cancer in solid organ transplant recipients. This meeting report is a summary of the novel findings discussed.

Cutaneous squamous cell carcinoma (CSCC) is the most common posttransplant cutaneous neoplasm. CSCC in the immunocompromised patient can have an aggressive course with a poor prognosis. The mechanisms underlying the development of posttransplant skin cancer are unknown. Studies have focused on the effects of immunosuppression in immunosurveillance of cutaneous neoplasms and in the keratinocyte changes following transplantation.

Immune Infiltrate in Skin Cancer

It has become increasingly apparent that whereas some arms of the immune system are important in controlling cancer via immunosurveillance, there are arms that are tumor promoting (1, 2). John Carucci presented studies examining the tumor microenvironment in transplant-associated SCC (TSCC), immune-competent SCC (SCC) and normal skin using immunohistochemistry, immunofluorescence microscopy and RT-PCR. T cell polarization in TSCC and SCC were examined by intracellular cytokine staining of T cells from human skin explants. TSCC and SCC are both associated with significantly higher numbers of CD3þ and CD8þ T cells compared with normal skin. TSCC showed a higher proportion of FoxP3þ regulatory T cells to CD8þ T cells compared with SCC and a lower percentage of IFN-g-producing CD4þ T cells. TSCC, however, had a higher percentage of IL-22 producing CD8þ T cells compared with SCC. TSCC showed more diffuse Ki67 and IL-22 receptor (IL-22R) expression (Table 1). IL-22 induced SCC proliferation in vitro despite serum starvation. Diminished cytotoxic T cell function in TSCC due to decreased CD8/regulatory T cell ratio may permit tumor progression. Increased IL-22 and IL-22R expression could accelerate tumor growth in transplant patients. IL-22 may be an attractive candidate for targeted therapy of transplant-associated SCC.

Table 1.

Immune infiltrate in squamous cell carcinoma in solid organ transplant recipients

Immune infiltrating cells in CSCC	TSCC	SCC
FoxP3+ regulatory T cells to CD8+ T cells	Increased	-
IFN-γ-producing CD4+ T cells	-	Increased
IL-22 producing CD8+ T cells	Increased	-
Ki67 expression	Increased	-
IL-22R expression	Increased	-

CSCC, cutaneous squamous cell carcinoma; SCC, immune-competent SCC; TSCC, transplant-associated SCC.

To date, the majority of studies on the etiology of posttransplant skin cancers have focused on the loss of cancer surveillance mechanisms stemming from postoperative immunosuppressive therapies that impair T cell activation. The innate immune system also plays a critical role in tumorigenesis and tumor progression. Macrophages, in particular, play a central role in the innate immune system with functions that include phagocytosis of pathogens and cellular debris and the secretion of cytokines and toxic products upon activation. Recent studies have demonstrated that tumor-associated macrophages (TAM) are correlated with a poor prognosis in SCCs of the head and neck, suggesting that macrophages may be contributing to tumor progression.

TAM-derived growth factors such as vascular endothelial growth factor (VEGF-A) are critical to tumor vascularization and growth. Further, an activation state, which is M2-like as characterized by the expression of arginase-1 and numerous scavenger receptors, has been described in TAMs. Oscar Colegio presented data based on the hypothesis that soluble factors produced by tumor cells induce a program in macrophages that is tumor promoting, a TAM-like state. Using syngeneic murine tumor models, he first determined that macrophages constitute a significant proportion of the tumor mass. Sorting these TAMs from tumors, he determined that TAMs are M2-like and express more VEGF-A than the combination of all other cells in the tumor. Studies of tumor-conditioned supernatant revealed that heat-stable soluble factors induce VEGF-A in bone marrow– derived and peritoneal macrophages via the transcription factor hypoxia-inducible factor 1-a (HIF1a). Analysis of the supernatant revealed a bioactive metabolite sufficient to induce VEGF-A via HIF1a in a dose-dependent manner. Colegio et al generated mice carrying a macrophage-specific deletion in HIF1a and observed no induction of VEGF-A in bone marrow–derived macrophages. He then determined that tumor supernatant and the bioactive metabolite were sufficient to induce a TAM-like state in bone marrow-derived and peritoneal macrophages. To determine the role of the TAM-like state in tumor progression, he generated mice carrying macrophage-specific deletions preventing the activation of macrophages to the TAM-like state. Syngeneic tumor models revealed a significant decrease in tumor mass in mice with macrophages unable to be activated to the TAM-like state versus control mice.

In these studies, Colegio identified a bioactive metabolite, produced in high concentrations by tumor cells, that reprograms macrophages to a tumor-promoting state, critical for tumor progression. Characterizing the core elements of these tumor-promoting pathways is critical to identifying targets and abrogating them to prevent tumor progression and metastasis—and current studies are correlating these findings in CSCCs.

Genetic Mutations in Squamous Cell Carcinoma

Zelmira Lazarova examined the role of microRNA (miRNA) signatures in the development of CSCC in solid organ transplant recipients (SOTR) and immunocompetent patients. Differential expression of 88 cancer-related miRNAs was analyzed using Human Cancer RT (2) miRNA PCR Arrays in 44 study participants with CSCC. The expression of miRNAs for all tumor samples was compared with those in 15 normal skin samples. Two miRNAs (miR-135b and miR-181a) were significantly up-regulated and 16 were significantly down-regulated in CSCCs. These miRNAs have been described as potent suppressors of tumor progression and metastasis. The findings suggest that CSCCs have a unique miRNA profiling pattern and provide basic information for further investigations of functional roles of miRNAs in CSCC development, progression and metastasis.

The role of human papillomavirus (HPV) in the development of CSCC is controversial. Transplant recipients are at risk for HPV infection developing diffuse verruca recalcitrant to conventional therapies. Lorna Mackintosh presented a new HPV therapeutic target involved in viral replication. The host cellular protein topoisomerase binding protein 1 (TopBP1) was identified as an interacting partner for HPV16 viral replication factor E2. A posttranslational mutant of HPV-16E2 was identified which fails to bind TopBP1 resulting in compromised viral replication; the equivalent mutation in HPV-8E2 resulted in similarly compromised replication. The E2-TopBP1 interaction is essential for the viral life cycle and is a potential new anti-viral target that may work across HPV types.

Challenges in the study of skin cancer include the lack of in vitro models for experimentation. Mariana Zamir has established a novel model system for studying skin cancer ex vivo. Samples from normal skin and nonmelanoma skin cancer were grown in organ culture. Assays for viability and apoptosis showed tissue viability for at least 72h after surgical removal. The system can be used as a model for human keratinocytic skin cancer and provides an available tool for assessing the efficacy and toxicity of potential therapeutic agent.

Skin Disease in Transplant Patients of Color

In the United States, approximately 40% of solid organ transplants are performed in patients with skin of color. Sarah Arron presented data from a multi-ethnic US population of transplant recipients. She demonstrated that Fitzpatrick skin type is an independent predictor of CSCC risk after transplantation. Fitzpatrick skin type is a classification system ranging from very fair skin, hair and eye color (Fitzpatrick Type I) to very dark skin, hair and eye color (Fitzpatrick Type VI). Arron discussed that Fitzpatrick skin type is a patient-reported measure of ability to tan and propensity to burn, rather than a physician estimate based on race or skin color.

Clinical Challenges in Solid Organ Transplant Recipients

Fiona Zwald and Clark Otley shared their experiences and insight in the development of a dermatology clinic dedicated to the treatment of transplant recipients. The intricacies of starting a dermatology clinic within a multidisciplinary transplant center at their respective institutions were discussed. The focus was on the unique needs of dermatology clinics and the collaboration of the dermatologist with the transplant team. The topics included the management of high-risk skin cancer patients. Risk factors leading to the development of nonmelanoma skin cancers are both modifiable and nonmodifiable (Table 2) (3). Risk assessment through consideration of these factors and skin cancer screening prior to transplantation allowed for early identification of high-risk patients. Reducing immunosuppression in transplant patients at risk for the development of posttransplant skin cancers was discussed.

Table 2.

Risk factors for squamous cell carcinoma in solid organ transplant recipients

Nonmodifiable risk factors	Modifiable risk factors
Pretransplant history of skin cancer	Sun exposure >1 h/day
Age >50 years old	Degree of immunosuppression
Sunburn as a child
Fair complexion (Fitzpatrick skin types I-III)
Reside in a hot climate for greater than 30 years

Cutaneous infections can be a diagnostic challenge in solid organ transplant patients. Immune system impairment can lead to rare opportunistic infections with a broad clinical presentation. Deniz Seckin discussed how infections may be associated with other infections, or masked by these, and may present subclinically and/or atypically for extended periods. The evolution may be particularly severe and diagnosis is often delayed. If not adequately diagnosed and treated, some infections can be fatal.

Working Group

The working groups consist of physicians and scientists collaborating on the completion of specific goals that are revisited every 2 years. The melanoma working group has previously published recommendations for transplantation following the diagnosis of melanoma (4). Fiona Zwald led the melanoma working group whose aim is to publish guidelines for appropriate wait times for solid organ transplantation following previous diagnosis of melanoma, Merkel cell carcinoma and CSCC. These guidelines will be compiled based upon literature review, best available data, consensus opinion and recently published updated National Comprehensive Cancer Network guidelines regarding survival and mortality statistics for such tumors in non-immunosuppressed patients.

Oscar Colegio led the immunology working group in reviewing immunosuppressive drug regimen modifications and reductions in SOTR with CSCC. The goal of the working group is to review the current literature on the mammalian target of rapamycin (mTOR) inhibitor sirolimus in reducing the frequency or severity of CSCC in SOTR (5–7). The working group concluded that revision of immunosuppression by switching from a calcineurin inhibitor to an mTOR inhibitor may be more effective in reducing the development of future SCCs after the development of a single SCC. This is in contrast to previous recommendations of considering revision of immunosuppression after the development of 5–10 SCC/year (8).

A focus of the International Transplant Skin Cancer Collaborative (ITSCC) members is the creation of a database/registry of SOTR with CSCC for a comprehensive study of outcomes following treatment. Roel Genders discussed a Skin Cancer in Organ Transplant Patients Europe (SCOPE) and ITSCC collaboration to prospectively examine SOTR with primary CSCC. The collaborative study examines the outcome of SOTR with CSCC at 2 and 5 years from cancer diagnosis. The outcomes measured will be defined as local, regional, in-transit and distant metastasis. The cohort is used to design a nested case–control study to determine patient and/or tumor risk factors for metastasis. Patient enrollment has begun. Centers interested in participating in the prospective study can contact Roel Genders (r.e.genders@lumc.nl) for further information.

Future Direction

SOTR have unique dermatologic challenges requiring a collaborative approach between the dermatologist and the transplant physicians. The focus of transplant dermatology has been on the development of posttransplant skin cancer, but as the transplant population increases, other dermatologic disorders present. Cutaneous infections can have a broad range of clinical presentations in the immunocompromised patient. High clinical suspicion and early intervention are important in infection treatment. Most dermatologic studies have focused on skin changes of fair-skinned transplant patients with Fitzpatrick I–III skin type. Patients with Fitzpatrick skin types IV through VI are also at risk for the development of posttransplant skin diseases requiring dermatologic care. Further study is needed to examine the unique needs of transplantation patients of color.

CSCC has significant patient morbidity and mortality in transplant patients. Decreased immune surveillance by innate and adapted immune cells has been investigated as a possible etiology for posttransplant skin cancer. The direct effect of immunosuppressants on keratinocyte development has been postulated as well. New keratinocyte models are proposed to examine the influence of immunosuppressants on keratinocyte function. SCC epidemiology studies have included single- or multi-center studies with a limited number of transplant patients. Methods for international collaboration between ITSCC and SCOPE members to prospectively study SCC in transplant patients with the goal of determining incidence and patient and/or tumor risk factors for metastasis were outlined.

Abbreviations

CSCC

cutaneous squamous cell carcinoma

HIF1a

hypoxia-inducible factor 1-a

HPV

human papillomavirus

IL-22R

IL-22 receptor

ITSCC

International Transplant Skin Cancer Collaborative

miRNA

microRNA

mTOR

mammalian target of rapamycin

SCC

immune-competent squamous cell carcinoma

SCOPE

Skin Cancer in Organ Transplant Patients Europe

SOTR

solid organ transplant recipients

TAM

tumor-associated macrophages

TopBP1

topoisomerase binding protein 1

TSCC

transplantassociated SCC

VEGF-A

vascular endothelial growth factor