The impact of preradiation residual disease volume on time to locoregional failure in cutaneous Merkel cell carcinoma--a TROG substudy.

This study evaluated the impact of margin status and gross residual disease in patients treated with chemoradiation therapy for high-risk stage I and II Merkel cell cancer (MCC).Data were pooled from 3 prospective trials in which patients were treated with 50 Gy in 25 fractions to the primary lesion and draining lymph nodes and 2 schedules of carboplatin based chemotherapy. Time to locoregional failure was analyzed according to the burden of disease at the time of radiation therapy, comparing patients with negative margins, involved margins, or macroscopic disease.Analysis was performed on 88 patients, of whom 9 had microscopically positive resection margins and 26 had macroscopic residual disease. The majority of gross disease was confined to nodal regions. The 5-year time to locoregional failure, time to distant failure, time to progression, and disease-specific survival rates for the whole group were 73%, 69%, 62%, and 66% respectively. The hazard ratio for macroscopic disease at the primary site or the nodes was 1.25 (95% confidence interval 0.57-2.77), P=.58.No statistically significant differences in time to locoregional failure were identified between patients with negative margins and those with microscopic or gross residual disease. These results must, however, be interpreted with caution because of the limited sample size.