Improved survival following lymphadenectomy for nodal metastasis from an unknown primary melanoma

Abstract

8515 Background: It is not possible to identify a primary site in 10–20% of melanoma patients presenting with palpable nodal metastases. The explanation for this phenomenon is unknown but could reflect an endogenous antimelanoma immune response that causes complete regression of the primary melanoma. If so, then these patients should have a better survival than patients whose primary melanoma has been identified. Methods: We reviewed our 13,000-patient prospective melanoma database (1971–2005) to identify patients managed with regional lymphadenectomy for palpable nodal metastases from unknown primary melanoma (MUP) or known primary cutaneous melanoma (MKP). Multivariate analysis was performed to identify prognostic factors significant for survival. MUP and MKP patients were then matched by significant covariates. Overall survival (OS) was estimated by Kaplan-Meier method and compared by log-rank analysis. Results: Among 1571 patients with palpable nodal metastases who underwent regional lymphadenectomy, multivariate analysis identified 5 significant covariates: age (HR=1.294, P=0.0017), sex (HR=1.335, P=0.0004), nodal tumor burden (HR=1.256, P<0.0001), decade of diagnosis (HR=0.989, P=0.0131), and unknown/known primary (HR=1.507; 95% CI=1.220 to 1.862; P=0.0001). Five-year OS was significantly higher for the 262 MUP patients than 1309 MKP patients (55±6% vs. 44±3%; P=0.0021). Computerized matching of MUP and MKP patients by four significant covariates (age, sex, nodal tumor burden, and decade of diagnosis) yielded 221 matched pairs. Median OS and 5-year OS rates were 165 months and 58±7%, respectively, for MUP as compared with 34 months and 40±6%, respectively, for MKP (P=0.0008). Conclusions: Our results strongly support the effectiveness of lymphadenectomy for nodal metastasis from MUP. Risk of death dropped significantly when regional lymphadenectomy was performed for metastases from MUP as compared with MKP. This result is compatible with an immunologic rejection of the primary melanoma due to a strong host antitumor immune response. Immunologic studies to identify cell-mediated and antibody components of this response are underway. No significant financial relationships to disclose.