The first sites of lymphatic drainage from primary melanoma tumour, sentinel nodes, are primarily found at major nodal basins in the axilla, groin or neck. However, there are minor nodal fields at triangular intermuscular space (TIS) in the back, epitrochlear in the arm and popliteal in the lower leg. In case of finding isolated metastasis of melanoma at these minor nodal fields, the treatment approach is yet little documented. This study assesses this subgroup of melanoma patients, their overall survival (OS) and recurrence free survival (RFS).

Retrospective database review of patients treated at Melanoma Institute Australia from 1980-2020 was performed. 18 years or older patients with isolated minor nodal field metastasis were included. Comparison of major and minor nodal fields metastasis RFS and OS was performed with matched cohort group using Kaplan-Meier method and log-rank test.

Of the 36 included patients 20 were male, 16 female, mean age 53 years at time of diagnosis. Median Breslow thickness was 2.1 (0 to 8.2). Sites of the metastases were epitrochlear (21/36, 58%), TIS (11/36, 31%) and popliteal (4/36, 11%). Treatments consisted of resection of the minor nodal field metastasis for 23/36 (63.9%) patients. Two (5.6%) patients received adjuvant radiation therapy and one (2.8%) adjuvant anti-PD1 immunotherapy. Radical lymphadenectomy of the onwards major nodal basin was performed for 1 (2.8%) patient in the ilioinguinal field and for 9 (25%) patients in the axilla. 15 out of 36 (41.7%) patients developed a further recurrence during follow-up (range 2 to 15 years).

There is a clear separation of the Kaplan-Meier curves indicating a more favourable prognosis in patients with isolated metastasis to a minor node field compared with a matched cohort of patients with metastasis to a major node field (p=0.0071).

Patients with minor nodal field metastasis might have better prognosis in terms of RFS compared to those with metastasis in major fields. Their treatment may be best managed with a personalised approach combining neoadjuvant immunotherapy where indicated, and limited surgery. For those achieving a lesser response, close observation rather than further dissection, would seem a reasonable approach.