Application of a Filtration- and Isolation-by-Size Technique for the Detection of Circulating Tumor Cells in Cutaneous Melanoma

Analysis of circulating tumor cells (CTC) in the peripheral blood of cutaneous melanoma patients provides information on the metastatic process and potentially improves patient management. The isolation by size of epithelial tumor cells (ISET) is a direct method for CTC identification in which tumor cells are collected by filtration as a result of their large size. So far, ISET has been applied only to CTC detection from epithelial cancer patients, and the technique has never been applied to cutaneous melanoma patients. We herein investigated the presence of CTC by ISET in the peripheral blood of 140 subjects (87 with cutaneous melanomas, 10 subjects undergoing surgery for melanocytic nevi, 5 patients with non-melanoma skin tumors, and 38 healthy volunteers). The identification of the cells trapped in filters as CTC was supported by positivity for immunohistochemical markers and for tyrosinase mRNA by real-time RT-PCR. CTC were neither detected in the controls nor in the in situ melanoma group. In contrast, CTC were shown in 29% of patients with primary invasive melanoma and in 62.5% of metastatic melanoma patients (P<0.01). CTC detection correlated with the presence of mRNA tyrosinase in blood samples, assayed by real-time RT-PCR (P=0.001). CTC detection corroborated by suitable molecular characterization may assist in the identification and monitoring of more appropriate therapies in melanoma patients.