Risk Factors for Positive Deep Pelvic Nodal Involvement in Patients with Palpable Groin Melanoma Metastases: Can the Extent of Surgery be Safely Minimized?

Background. Patients with palpable melanoma groin metastases have a poor prognosis. There is debate whether a combined superficial and deep groin dissection (CGD) is necessary or if superficial groin dissection (SGD) alone is sufficient. Aim. The aim of this study was to analyze risk factors for deep pelvic nodal involvement in a retrospective, multicenter cohort of palpable groin melanoma metastases. This could aid in the development of an algorithm for selective surgery in the future. Methods. This study related to 209 therapeutic CGDs from four tertiary centers in The Netherlands (1992-2013), selected based on complete preoperative imaging and pathology reports. Analyzed risk factors included baseline and primary tumor characteristics, total and positive number of inguinal nodes, inguinal lymph node ratio (LNR) and positive deep pelvic nodes on imaging (computed tomography [CT] +/- positron emission tomography [PET], or PET -low-dose CT). Results. Median age was 57 years, 54 % of patients were female, and median follow-up was 21 months (interquartile range [IQR] 11-46 months). Median Breslow thickness was 2.10 mm (IQR 1.40-3.40 mm), and 26 % of all primary melanomas were ulcerated. Positive deep pelvic nodes occurred in 35 % of CGDs. Significantly fewer inguinal nodes were positive in case of negative deep pelvic nodes (median 1 [IQR 1-2] vs. 3 [IQR 1-4] for positive deep pelvic nodes; p < 0.001), and LNR was significantly lower for negative versus positive deep pelvic nodes [median 0.15 (IQR 0.10-0.25) vs. 0.33 (IQR 0.14-0.54); p < 0.001]. A combination of negative imaging, low LNR, low number of positive inguinal nodes, and no extracapsular extension (ECE) could accurately predict the absence of pelvic nodal involvement in 84 % of patients. Conclusions. Patients with negative imaging, few positive inguinal nodes, no ECE, and low LNR have a low risk of positive deep pelvic nodes and may safely undergo SGD alone.