Circulating Tumor Cell Cultures as a Predictive Marker during Salvage Therapy of Refractory Merkel Cell Carcinoma with Chemotherapy and Electron Beam Radiation

Metastatic Merkel Cell carcinoma (MCC) is a highly unusual and aggressive skin cancer that presents as a small, pink to violet skin lesion and metastasizes early in its growth. Metastatic MCC is generally treated with small cell lung cancer chemotherapy regimens, because the tumor consists of neuroendocrine cells, but patients generally do not have durable responses. The pathogenesis of MCC has recently been attributed to the Merkel Cell polyoma virus. This virus activates the cellular retinoblastoma oncoprotein and cell cycle machinery, triggering continual cellular proliferation. A 77-year-old man developed extensive MCC metastases, involving more than one fourth of his scalp and numerous cervical lymph nodes. Following failure of initial chemotherapy and radiation, effective palliation was achieved by using a sequence of electron-beam radiotherapy, low dose gemcitabine, and etoposide, resulting in significant periods of tumor regression and prolonged survival. A novel circulating tumor cell (CTC) culture assay was performed on four separate clinic visits during the treatment period. Tumor colonies were cultured from the patient’s peripheral blood and CTC colony counts were correlated with clinical treatment response. Not only did the patient respond to palliative cell cycle directed chemotherapy and electron beam radiation, but we demonstrated that CTC can be cultured from peripheral blood of MCC patients and serve as a predictive marker to monitor treatment response.