Sentinel lymph node biopsy in clinically node-negative Merkel cell carcinoma: the Westmead Hospital experience.

Background: Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous malignancy with a propensity to metastasize to regional lymph nodes. Sentinel lymph node biopsy (SLNB) in patients with clinically node-negative MCC has been utilized to identify patients with subclinical nodal metastases. This study aims to review the accuracy of SLNB in MCC and to evaluate the impact of SLNB on management.

Methods: Patients with clinically node-negative MCC who underwent SLNB were identified from a prospective database of patients treated at the Westmead Hospital, Sydney, between 1998 and 2017. Data from these patients were reviewed and analysed.

Results: Forty-one patients were identified: 28 men and 13 women, median age 70 years. Median duration of follow-up was 27 months. Sixteen (39%) patients had a positive SLNB and all underwent nodal treatment which consisted of radiotherapy (n = 13), completion lymphadenectomy and adjuvant radiotherapy (n = 2), and completion lymphadenectomy alone (n = 1). Following negative SLNB, 24 of 25 patients did not undergo further nodal treatment. The false-negative rate was 16% as three patients developed in-field nodal recurrence subsequent to a negative SLNB. At last follow-up, 29 patients had no evidence of disease, six were alive with disease and three had died from other causes. Three SLN-positive patients have died of MCC.

Conclusion: SLNB has a high rate of positivity and can improve the accuracy of staging and prognostication in MCC, and guide management. The relatively low risk of a false-negative SLNB justifies close observation in SLNB-negative patients.