Abstract
Subcapsular deposits of nevoid melanoma in a lymph node may be a challenging histologic distinction from nodal nevus, especially when primary melanoma is thin, and deposits are large. We present such a case of a 43-year-old female who was diagnosed with nevoid melanoma (arising in a background of nevus) on the right scapula with Breslow depth of 0.8 mm. The patient underwent wide local excision and sentinel node sampling. While there was no residual melanoma, one of the sentinel lymph nodes showed multiple, large subcapsular deposits of small, monomorphic melanocytes, reaching up to 0.8 mm in greatest dimension. The morphologic comparison of these melanocytes to the primary melanoma was not helpful as cells looked similar. SOX10 and Melan-A stains highlighted the nodal melanocytes but Ki-67 and PRAME stains were negative. A retrospective PRAME stain was performed on primary melanoma that highlighted the melanoma cells, but nevomelanocytes were negative. Thus, we were able to rule out metastatic nevoid melanoma, and the diagnosis of an incidental subcapsular melanocytic nevus was made. This was an interesting case of alarmingly large deposits of nevomelanocytes in the lymph node and PRAME staining proved to be useful. Alternatively, molecular testing using prime editing can be used to compare the melanoma cells with nevus.
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