N-ratio: A novel independent prognostic factor for patients with stage-III cutaneous melanoma

Background: In this study, we tested the hypothesis that the ratio between metastatic and excised lymph nodes ("N-ratio") might have an independent prognostic value in patients with TNM stage-III cutaneous melanoma. Methods: The clinical records of 213 melanoma patients who had undergone radical lymph node dissection (RLND) and were found to harbor pathology-proven metastatic disease were used for analysis. The following clinico-pathological variables were considered for the prognostic study: patient's age and sex, primary tumor site, tumor thickness, Clark's level, ulceration, absolute number of positive lymph nodes, total number of excised lymph nodes, TNM stage (IIIA, IIIB, IIIC), and N-ratio (N-ratio A, <= 10%; N-ratio B, 10-25%; N-ratio C, > 25%). Results: Patients were categorized into three N-ratio classes according to the percentage of metastatic lymph nodes (N-ratio A, n = 94; N-ratio B, n = 95; N-ratio C, n = 24). The mean follow-up was 40 months. At univariate survival analysis, tumor thickness (P < 0.0001), ulceration (P = 0.046), Clark's level (P = 0.0002), number of positive lymph nodes (P < 0.0001), TNM stage (P < 0.0001), and N-ratio (P < 0.0001) were significantly associated with overall survival (OS). Interestingly, the Cox proportional hazard model showed that, along with tumor thickness (HR 1.069, P = 0.008) and TNM stage (HR 1.696, P = 0.015), N-ratio (HR 1.578, P = 0.012) also independently predicted OS. Conclusions: N-ratio is a novel easy-to-obtain independent prognostic factor for melanoma patients with lymph node metastases and might provide clinicians with additional information suitable for patient stratification while choosing adjuvant treatment. Validation of these results in larger prospective series is warranted to implement N-ratio in the routine clinical setting.