Incidence and patterns of lymphatic drainage to the epitrochlear and popliteal sentinel lymph nodes in malignant melanoma of the distal extremities: a single-institution retrospective study.

Background: In most cutaneous melanomas of the distal extremity, sentinel lymph nodes (SLNs) are identified in the axillary or inguinal basin; however, they may be occasionally found in the epitrochlear or popliteal basins. The incidence and patterns of lymphatic drainage to the epitrochlear or popliteal SLNs are unclear.

Methods: To clarify the incidence and clinical characteristics of melanoma draining to these ectopic SLNs, we performed a retrospective study of the patients with distal extremity melanoma who underwent SLN biopsy at the National Cancer Center Hospital between April 2010 and December 2017.

Results: We identified 27 patients with melanoma of the distal upper extremity and 113 patients with melanoma of the distal lower extremity. All patients with distal upper and lower extremity melanomas had SLNs in the axillary and inguinal basins. Epitrochlear SLNs were found in 14.8% (4/27) of the patients with upper extremity melanoma, and the frequency increased by 36.4% (4/11) when the primary melanoma was located in the basilic vein area (P = 0.00188). Popliteal SLNs were found in 21.2% (24/113) of the patients with lower extremity melanoma, and the frequency increased by 37.9% (22/58) when the primary melanoma was located in the lesser saphenous vein area (P < 0.0001).

Conclusion: The incidence of SLNs identified in the epitrochlear or popliteal basin is not uncommon, and physicians need to be aware of these ectopic SLNs, especially when the primary melanoma is located in the basilic vein or lesser saphenous vein areas accordingly.