Does adjuvant radiotherapy increase survival in patients with Merkel cell carcinoma of the skin?

Background Merkel cell carcinoma (MCC) is a relatively rare, but aggressive skin cancer, with a high propensity for local recurrence and regional and distant metastases. Most data on MCC are from sing le-institution retrospective analyses, making it difficult to assess the role of adjuvant radiation therapy in the treatment of this disease. Surgical resection of the primary tumor with extensive margins is the main form of therapy. Objective To analyze the role of adjuvant radiotherapy in patients undergoing surgical excision for MCC. Design and intervention Data extracted from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute were used to identify patients diagnosed with MCC between 1973 and 2002. Information regarding patient demographics, treatment modalities and tumor characteristics was reviewed. Tumor characteristics documented included site of primary tumor, size at presentation, nodal status of the disease and whether distant metastases were present. Information was available on what surgery was performed at the primary site and lymph nodes, and on the use of adjuvant radiation therapy, but not on the use of chemotherapy or the use of sentinel node biopsy. Outcome measure The primary end point of the trial was overall survival. Results The SEER registry contained 1,665 cases of MCC over the time period reviewed, with surgery being a component of therapy in 89% of cases (n = 1,487). The overall median follow-up was 40 months and the overall median survival was 49 months. Excision or re-excision or minor amputation without lymph-node dissection was performed in 82% (n = 1,214) of the surgical cohort, and extended surgery with lymph-node dissection or major amputations was performed in 10% (n = 135) of this cohort. External-beam radiation was the type of radiotherapy most frequently used (98%). Median overall survival was 63 months in patients who received adjuvant radiation therapy and 45 months in patients who did not (P=0.0002). On multivariate analysis, the association of adjuvant radiation therapy with survival was statistically significant (P=0.0122). The use of adjuvant radiation therapy was associated with improved overall median survival across all age groups. When the results were stratified by tumor size, adjuvant radiation therapy was associated with an improved overall median survival in patients with tumors <1 cm in size (from 48 to 93 months P=0.0447), in patients with tumors 1-2cm in size (from 52 to 86 months; P=0.0126) and in patients with tumors larger than 2 cm (from 21 to 50 months; P=0.0003). Conclusion There was a positive association between adjuvant radiation therapy and overall survival, which remained statistically significant on multivariate analysis.