A Rare Case of Merkel Cell Carcinoma Presented with Lambert Eaton Myasthenic Syndrome without Cutaneous Findings

Circulating tumor DNA offers a “real-time†tool for serial monitoring of tumor genomes by providing accessible genetic biomarkers for cancer diagnosis, prognosis, and response to therapy; thus, circulating tumor DNA has progressively become routinely used in clinical oncology. Another type of liquid biopsy focuses on analysis of circulating tumor cells (CTCs), which is potentially more practical for obtaining genome-wide information and facilitating heterogeneity analysis. The Cell Search System is the only validated method for CTC detection that has been approved by the Food and Drug Administration. Based on this principle, we enrolled a group of patients with newly diagnosed and locally advanced or metastatic non-small cell lung cancer, CTCs were isolated by micromanipulation followed by whole-genome amplification, then analyzed by quantitative PCR for epidermal growth factor receptor (EGFR) mutation. In 63% of these patients ≥1 CTC was isolated. We then investigated whether the captured CTCs were suitable for molecular characterization. Four patients, the amplified CTC genomic DNA was further analyzed that proved with copy number variation. However, only two of these patients’ CTCs showed exactly specific EGFR mutations identical to those of the primary tumor, while the others showed clearly different mutations from the primary tumor. Conclusions: These preliminary results suggest that the use of CTCs may be feasible for heterogeneity analysis of tumor mutations.