Molecular and immune targets for Merkel cell carcinoma therapy and prevention

Advancing Treatment Options for Merkel Cell Carcinoma: A Review of Tumor-Targeted Therapies

Although rare, Merkel cell carcinoma (MCC) is a highly aggressive and increasingly prevalent neuroendocrine cancer of the skin. While current interventions, including surgical resection, radiation, and immunotherapy have been employed in treating many patients, those who remain unresponsive to treatment are met with sparse alternatives and a grim prognosis. For this reason, it is of interest to expand the repertoire of available therapies for MCC patients who remain resistant to current primary interventions. Recently, our improved mechanistic understanding of aberrant cell signaling observed in both MCPyV-positive and -negative MCC has facilitated exploration into several small molecules and inhibitors, among them receptor tyrosine kinase inhibitors (TKIs) and somatostatin analogs (SSAs), both of which have positively improved response rates and reduced tumor volumes upon application to treatment of MCC. The introduction of such targeted therapies into treatment protocols holds promise for more personalized care tailored towards patients of diverse subtypes, thereby improving outcomes and mitigating tumor burden, especially for treatment-resistant individuals. In this review, we characterize recent findings surrounding targeted treatments that have been applied to MCC and provide an overview of emerging perspectives on translatable options that can be further developed to offer additional therapeutic avenues for patients with the disease.

The emerging role of miRNAs in Merkel cell carcinoma pathogenesis: Signaling pathway crosstalk

Merkel cell carcinoma (MCC) is an uncommon invasive form of skin cancer that typically manifests as a nodule on the face, head, or neck that is flesh-colored or bluish-red in appearance. Rapid growth and metastasis are hallmarks of MCC. MCC has the second-greatest mortality rate among skin cancers after melanoma. Despite the recent cascade of molecular investigations, no universal molecular signature has been identified as responsible for MCC's pathogenesis. The microRNAs (miRNAs) play a critical role in the post-transcriptional regulation of gene expression. Variations in the expression of these short, non-coding RNAs have been associated with various malignancies, including MCC. Although the incidence of MCC is very low, a significant amount of study has focused on the interaction of miRNAs in MCC. As such, the current survey is a speedy intensive route revealing the potential involvement of miRNAs in the pathogenesis of MCC beyond their association with survival in MCC.

BRCA1/2 Pathogenic Variants Are Not Common in Merkel Cell Carcinoma: Comprehensive Molecular Study of 30 Cases and Meta-Analysis of the Literature

Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous neuroendocrine cancer. Management of advanced MCC is mainly based on immune-checkpoint inhibitors. The high failure rate warrants an investigation of new therapeutic targets. The recent identification of BRCA1 or BRCA2 (BRCA1/2) mutations in some MCC raises the issue of the use of poly-(ADP-Ribose)-polymerase inhibitors in selected advanced cases. The main objective of our study is to determine the accurate frequency of BRCA1/2 pathogenic variants. We studied a series of 30 MCC and performed a meta-analysis of BRCA1/2 variants of published cases in the literature. In our series, we detected only one BRCA2 pathogenic variant. The low frequency of BRCA1/2 pathogenic variants in our series of MCC (3%) was confirmed by the meta-analysis of BRCA1/2 variants in the literature. Among the 915 MCC from 13 published series studied for molecular alterations of BRCA1/2, only 12 BRCA1/2 pathogenic mutations were identified (1-2% of MCC), whereas many other BRCA1/2 variants were variants of unknown significance or benign. BRCA1/2 pathogenic variants are uncommon in MCC. However, in BRCA-mutated MCC, poly-(ADP-Ribose)-polymerase inhibitors might be a valuable therapeutic option requiring validation by clinical trials.

Molecular and immune targets in cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer and often confers a good prognosis. Though surgery is the gold standard of treatment, unresectable or metastatic disease can necessitate systemic therapy. Of systemic agents, there is increasing interest in the use of immunotherapies and targeted therapy. Further study into the driver mutations in cSCC has identified opportunities for targeted therapy. In this review, we discuss both current and investigational immune and molecular targets of therapy for cSCC.

Identification of natural product modulators of Merkel cell carcinoma cell growth and survival

Merkel cell carcinoma (MCC) is a rare, but aggressive skin cancer the incidence of which has increased significantly in recent years. The majority of MCCs have incorporated Merkel cell polyomavirus (VP-MCC) while the remainder are virus-negative (VN-MCC). Although a variety of therapeutic options have shown promise in treating MCC, there remains a need for additional therapeutics as well as probes for better understanding MCC. A high-throughput screening campaign was used to assess the ability of > 25,000 synthetic and natural product compounds as well as > 20,000 natural product extracts to affect growth and survival of VN-MCC and VP-MCC cell lines. Sixteen active compounds were identified that have mechanisms of action reported in the literature along with a number of compounds with unknown mechanisms. Screening results with pure compounds suggest a range of potential targets for MCC including DNA damage, inhibition of DNA or protein synthesis, reactive oxygen species, and proteasome inhibition as well as NFκB inhibition while also suggesting the importance of zinc and/or copper binding. Many of the active compounds, particularly some of the natural products, have multiple reported targets suggesting that this strategy might be a particularly fruitful approach. Processing of several active natural product extracts resulted in the identification of additional MCC-active compounds. Based on these results, further investigations focused on natural products sources, particularly of fungal origin, are expected to yield further potentially useful modulators of MCC.

Effect of Sentinel Lymph Node Biopsy and LVI on Merkel Cell Carcinoma Prognosis and Treatment

OBJECTIVE

Prognostic factors and optimal treatment approaches for Merkel cell carcinoma (MCC) remain uncertain. This study evaluated the influences of sentinel lymph node (SLN) biopsy and lymphovascular invasion (LVI) on treatment planning and prognosis.

STUDY DESIGN

Retrospective cohort study.

METHODS

Stage 1 to 3 MCC patients treated 2005 to 2018. Predictors of nodal radiation were tested using logistic regression. Predictors of recurrence-free, disease-specific, and overall survival were tested in Cox proportional hazard models.

RESULTS

Of 122 patients, 99 were without clinically apparent nodal metastases. Of these, 76 (77%) underwent excision and SLN biopsy; 29% had metastasis in SLNs, including 20% of MCCs 1 cm or less. Primary tumor diameter, site, patient age, gender, and immunosuppressed status were not significantly associated with an involved SLN. Among patients who underwent SLN biopsy, 13 of 21 (62%) MCCs with LVI had cancer in SLNs compared with 14 of 44 (25.5%) without LVI (P = .003). Although local radiation was common, nodal radiation was infrequently employed in SLN negative (pathologic N0) patients (21.8% vs. 76.2% for patients with SLN metastases, P = .0001). Survival of patients with positive SLNs was unfavorable, regardless of completion lymphadenectomy and/or adjuvant radiation. After accounting for tumor (T) and node (N) classification, age, immunosuppression, and primary site, a positive SLN and LVI were independently associated with worse survival (LVI/recurrence-free survival [RFS]: hazard ratio [HR] 2.3 (1.04-5, P = .04; LVI/disease-specific survival [DSS]: HR 5.2 (1.8-15, P = .007); N1a vs. pN0/RFS HR 3.6 (1.42-9.3, P = .007); DSS HR5.0 (1.3-19, P = .17).

CONCLUSION

SLN biopsy assists in risk stratification and radiation treatment planning in MCC. LVI and disease in SLNs, independently associated with worse survival, constitute markers of high-risk disease warranting consideration for investigational studies.

LEVEL OF EVIDENCE

III Laryngoscope, 131:E828-E835, 2021.