Unusual Histopathological Patterns in Melanocytic Nevi With Some Previously Undescribed Patterns

Rosette-like formations in melanocytic neoplasms: A case report and literature review

Homer-Wright-like rosettes are a common finding in neural tumors but seldom seen in melanocytic nevi and melanoma. We report a case of a 23-year-old male with a compound melanocytic nevus with such rosette-like structures and summarize the current literature on this histopathological feature in melanocytic neoplasms. A symmetric, well-circumscribed, compound nevus consisting of aggregations of epithelioid melanocytes with eccentric nuclei and central eosinophilic cytoplasm, resembling Homer-Wright rosettes, was present on biopsy. Immunohistochemical stains strongly supported a melanocytic entity and were negative for NTRK1/2/3, a fusion protein potentially associated with rosette-like structures. We found 17 other cases of benign melanocytic nevi, including 9 atypical Spitz tumors and 6 Spitz nevi, and 11 malignant melanomas, including 3 Spitz melanomas and 4 metastases. We observed remarkable diversity among lesion morphologies containing rosettes, as well as level of prominence and cytology of the rosettes themselves. This case illustrates the morphologic malleability of neural-crest-derived lesions to share microscopic and phenotypic attributes.

Interesting overlooked findings in melanocytic nevi

Since histological analysis is the gold standard for melanoma diagnose, to understand possible findings in nevi is the first step to avoid diagnostic errors. The aim of this paper is to describe several histological features that can be found in nevi and may be misunderstood or overlooked. Histological findings were organized into two groups: 1- adaptive findings (neurotization, sebaceous alteration, adipose metaplasia, amyloid deposition and calcifications, pseudovascular lacunae), 2- findings that can occasionally be associated with malignancy (suspicious for angiolymphatic invasion, perineural infiltration, deep mitosis, muscle infiltration). Each finding by itself does not mean that lesion is malignant. We have selected 13 cases of benign intradermal or compound melanocytic nevi excised for aesthetical purposes from our collection to illustrate possible overlooked findings in melanocytic nevi.

Chondroid atypical spitzoid melanocytic tumor

Chondroid stromal change is very rare in melanocytic nevi. We present a severely atypical symmetrical Spitz tumor on the right arm of a 24-years-old man. It showed maturation and occasional mitotic figures. The melanocytes were intermingled with cartilaginous stroma. The Ki67 proliferative rate was 5%. It was weakly positive for p16 and negative for BRAF/V600E. BAP1 expression was preserved. PCR for Myriad myPath^® Melanoma test was also negative.