BACKGROUND
Quantitation of circulating tumor cells (CTCs) has utility in managing breast, colon, and prostate carcinomas.
OBJECTIVE
We sought to determine whether a commercially available CTC assay provides prognostic information in Merkel cell carcinoma (MCC), insight into treatment responses, or both.
METHODS
We analyzed CTCs in 52 specimens from 34 patients with MCC.
RESULTS
The presence of CTCs correlated with extent of disease at blood draw (P = .004). Among 15 patients with regional nodal disease, CTC-negative patients had 80% disease-specific survival at 2 years after the test, versus 29% for CTC-positive patients (P = .015). Among the entire cohort, those without CTCs had 72% MCC-specific survival whereas CTC-positive patients had 25% survival (n = 34, median follow-up 19 months, P = .0003). Fifty seven percent of patients with MCC had a cytokeratin “dot” visible in 20% or more of CTCs, a feature that was absent among CTCs from other carcinomas (0 of 13 cases).
LIMITATIONS
CTC assay was performed at variable times after diagnosis and heterogeneity in extent of disease affects interpretability of the data.
CONCLUSION
CTC detection in MCC is feasible and appears to add prognostic information, particularly in patients with regional nodal disease. It may also assist clinical management in certain situations, including differentiating metastatic MCC cells from those of other carcinomas.