Dr. Wolf said the diagnostic challenge is to distinguish Merkel cell carcinoma from metastatic small cell carcinoma of the lung, melanoma, and lymphoblastic lymphoma. This can be done immunohistologically on the basis of positive staining for cytokeratin 20 and neurofilament, which is unique to Merkel cell carcinoma among these cancers. Also, most Merkel cell carcinomas will stain positive for CM2B4, which recognizes MCPyV, while the other malignancies will not.
Current guidelines recommend surgery with wide margins along with routine sentinel lymph node biopsy. Radiation therapy to the tumor bed and regional lymph nodes is recommended when nodes are positive.
“Surgery is the best and I would say the only good treatment for Merkel cell carcinoma,” according to Dr. Fernandez-Figueras.
Chemotherapy is palliative. The agents used are similar to those employed in small cell lung carcinoma, including cyclophosphamide, doxorubicin, vincristine, and cisplatin with or without etoposide.
Dr. Wolf said there is considerable interest in trying targeted therapy for Merkel cell carcinoma. A Phase II study of the bcl-2 antisense agent oblimersen (Genasense) disappointingly showed no objective responses in patients with advanced disease (Am. J. Clin. Oncol. 2009;32:174-9). However, there is a case report of an excellent result with pazopanib (Votrient) in a patient with metastatic Merkel cell carcinoma (J. Clin. Oncol. 2009;27:e97-100; PMID 19564526).
Drs. Wolf and Fernandez-Figueras reported they had no financial conflicts.