Giant Dedifferentiated Melanoma Mimicking Soft Tissue Sarcoma with Loss of Conventional Melanocytic Markers: Diagnostic Utility of PRAME and BRAF V600E Immunohistochemistry

Dedifferentiated melanoma can lose conventional melanocytic markers and mimic soft tissue sarcoma, complicating diagnosis. In some cases, next-generation sequencing (NGS) has been required to secure the diagnosis. We report a giant (>10 cm) sarcomatoid melanoma in which diffuse PRAME immunohistochemistry raised suspicion and concordant BRAF V600E positivity in both the sarcomatoid tumor and an associated nevus established the diagnosis of melanoma. This two-step, widely accessible workflow, PRAME screening followed by targeted BRAF V600E testing, enabled diagnosis without comprehensive NGS and may aid similarly challenging sarcomatoid cutaneous tumors.