Background: Although the number of excised LNs has been associated with patient prognosis in many solid tumors, this association has not been widely investigated in cutaneous melanoma. This study aims to evaluate the association between the number of excised regional lymph nodes (LNs) and melanoma-specific survival.

Patient and methods: Clinico-pathological data from 2507 patients with LN metastasis treated at nine Italian centers were retrospectively collected.

Results: The number of excised LNs correlated with younger age (P < 0.001), male sex (P < 0.001), neck LN field (P < 0.001), LN micrometastasis (P < 0.001) and number of positive LNs (P < 0.001). The number of excised LNs was an independent prognostic factor (HR = 0.85; P = 0.002) after adjustment for other staging features. Upon subgroup analysis, the number of excised LNs had a significant prognostic value in patients bearing 1.01-2.00 mm (HR = 0.79; P = 0.032) and 2.01-4.00 mm (HR = 0.71; P < 0.001) thick melanomas, primary tumors showing ulceration (HR = 0.86; P = 0.033) and Clark level V of invasion (HR = 0.86; P = 0.010), LN micrometastasis (HR = 0.83; P = 0.014) and two to three positive LNs (HR = 0.71; P = 0.001). Finally, this study investigated the influence of the number of excised LNs on patient staging: only when ≥11 nodes were excised the AJCC N stage could stratify prognosis (P < 0.001). Considering the number of excised LNs for each lymphatic field, at least 14, 11, 10 and 12 LNs were needed to stage patients according to the AJCC N stage after a lymphadenectomy of the neck, axilla, inguinal and ilioinguinal LN fields, respectively.

Conclusions: The number of excised LNs can be considered for risk stratification of patients with regional LN metastasis from cutaneous melanoma. We demonstrated that a minimum number of LNs is required for the correct staging of patients. Further research is needed to evaluate the effectiveness of the minimum number of LNs to be dissected.