Background: Controversy exists regarding the predictive ability of a negative sentinel lymph node biopsy (SLNB) and the use of adjuvant radiation in Merkel cell carcinoma (MCC).
Methods: Retrospective study of patients with MCC undergoing SLNB at Mayo Clinic from 1995 to 2011. Cumulative incidence (CI) of regional recurrence and death from MCC, respectively, were estimated taking into account the competing risk of death from other causes and compared between groups using Gray's test.
Results: A total of 111 (74 %) of 150 SLNB were negative and comprised our study group. There were 15 regional recurrences, and the CI of a regional recurrence was 5.1, 15.0, and 16.6 % at 1, 3, and 5 years, respectively, after initial surgery. Nine patients (8 % of all patients) experienced a same nodal basin recurrence after a negative SLNB. Among 14 patients who received nodal radiation, the CI of a regional recurrence was 0 and 9.1 % at 1 and 3 years, respectively, compared to 5.8 and 15.5 %, respectively, among the 97 who did not receive nodal radiation (p = 0.45). Male sex was the only characteristic predictive of regional recurrence after a negative SLNB; the CI at 3 years was 21.3 versus 0 % in men and women, respectively (p = 0.007). Head and neck location was not associated with a higher risk of recurrence or an improvement in regional recurrences after radiation.
Conclusions: Same nodal basin recurrences are uncommon after SLNB in MCC, and regional nodal irradiation can be avoided in the setting of successful sentinel lymph node mapping and a negative SLNB.