Potential applications of circulating melanoma cells (CMCs) expressing γ-H2AX.

Abstract

e22036 Background: The CMC analysis was recently improved by the CellSearch platform that offers an accurate (and reproducible) assessment of tumor burden, to be used as prognosticator and predictor of treatment response.Moreover, not only decreased total circulating cells numbers but also increased fraction of apoptotic cells may represent response-related markers. To monitor changes in the balance between live and apoptotic Circulating Tumor Cells (CTCs) ( Rossi, Basso et al. 2010 ) during therapy, a novel CTCs assay with a companion algorithm (the ΔAUC) was reported to be a pharmacodynamic marker, as documented by consistent radiological findings in MBC and mRCC patients. Methods: Fluorescent anti γ-H2AX mAb (specific for the phosphorylated form of H2AX) was integrated in the standard CMC assay to assess DNA damage and to measure cell viability and apoptosis in spreading melanoma cells. The integrated test was developed using MCF-7 and SK23mel cells line and tested in melanoma patients. From June-2011 till now, basal blood samples from 64 patients (pts) in stage IV were collected; median age 62 (range: 27-85). Both considering the cost of the CMC assay and the little already known about this new method in melanoma, to evaluate the feasibility of CMC retrieval and ΔAUC calculation an interim analysis was specified in the study protocol and conducted at September 2012 on the first 40 pts. Results: At baseline, in Padova’s cohort 72.6% of pts are CMC-positive. The CMC number ranged from 1 to 94. The γ-H2AX-positive CMCs ranged from 0% to 100% (median 67%). Shorter median Progression-free survival PFS was observed for patients who had > 2 CMCs (n=26, 162 days) compared with < 2 CMCs patients (n=14, 203 days, P value = 0.0270). No significant differences were found with the ΔAUC criterion (i.e. exceeding live vs apoptotic CMCs). Furthermore, a significant association was found between CMC-positive status at baseline and disease sites at progression (visceral and CNS, Chi-square = 8,521 with 3 df, P value = 0.036). Conclusions: Accrual is ongoing. Updated data including evaluations on prognostic value of total and apoptotic CMCs and correlation with clinical stage, tumor burden, metastatic sites and survival will be available and presented at the meeting.