Merkel cell carcinoma: The prognostic implications of an occult primary in stage IIIB (nodal) disease

Background: Merkel cell carcinoma is a highly aggressive cutaneous malignancy with a high rate of lymph node and distant metastatic disease. Approximately one third of patients present with stage IIIB (nodal) disease. Objective: This cohort study was performed to analyze the outcome of patients with stage IIIB disease with or without an occult primary. Methods: The details of 91 patients with stage IIIB (nodal) Merkel cell carcinoma treated curatively between 1985 and 2010 at 3 tertiary referral hospitals in Australia were reviewed. Kaplan-Meier plots were used with the primary end point being overall survival. Secondary end points were disease-free survival and relapse-free survival. A multivariate Cox regression analysis was performed for known prognostic factors. Results: Of 91 patients with stage IIIB (nodal) disease, 36 (40%) had an occult primary. A total of 78 patients (86%) had surgery and 79 patients (87%) had definitive or adjuvant radiotherapy. With a median follow-up of 4.3 years, those with an occult primary did significantly better in terms of overall survival, disease-free survival, and relapse-free survival. On multivariate analysis, occult primary and patient age were the only factors predicting survival with hazard ratios of 0.30 (95% confidence interval 0.13-0.67) and 1.64 (95% confidence interval 1.13-2.38), respectively. Limitations: This is a retrospective study over several decades with patients treated using various modalities. Conclusion: This study indicates that for patients with stage IIIB (nodal) Merkel cell carcinoma, the presence of an occult primary confers a significantly better prognosis that may have implications in the future staging and treatment of patients with stage III disease. (J Am Acad Dermatol 2012;67:395-9.)