Capsular nevus in melanoma sentinel lymph node: a difficult diagnosis with prognostic implication

Abstract

Abstract: 

The finding of melanoma metastasis in sentinel lymph node is an ominous prognostic sign and a strong predictor of overall survival. Current data have shown that patients with nevus cells in sentinel lymph nodes do not require additional therapy as their prognosis has been shown to be similar to that of patients with negative lymph nodes. Distinguishing between benign capsular nevi and metastatic melanoma is problematic from a diagnostic point of view. The use of an immunohistochemical panel for melanocytic lesions is usually of limited value in differentiating with metastatic melanoma and the diagnosis is usually based mainly on histomorphological findings.

53-year-old man, diagnosed with nodular variant of melanoma with BRAF V600E mutation in exon 15, located on the back and excised in November 2020; with surgical margin extension in February 2021 due to compromised surgical limit and with sentinel lymph node removal. Right and left axillary nodes were removed, the first measured 1.5 x 1 x 0.6 cm and the left ones were two: the largest measured 2 x 1.5 x 1 cm and the smallest 1 x 0.5 x 0.5 cm.

Microscopy: reactive lymphoid hyperplasia and abundant black tattoo ink at sinus location were observed in the left nodes, while in the right one a proliferation of nevus-like cells arranged in nests was observed, at intracapsular location, and immunohistochemistry was Melan-A and HMB-45 positive, with a cell proliferation index (% Ki-67) of 1 - 5%. Consultation with local dermatopathologists was made and the diagnosis was intracapsular melanocytic nevus.

The lack of standardized criteria to distinguish between nevus cells and melanoma poses a diagnostic problem. To avoid misdiagnosis and unnecessary therapy, obtaining a second opinion from additional histopathologists would be beneficial. The use of tissue morphology in conjunction with immunohistochemical staining may be the best way to make the most accurate diagnosis. The use of molecular tests to determine characteristic somatic mutations of melanoma will probably help in the near future to facilitate the distinction between capsular nevi and metastatic melanoma.