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Case Reports

Abstract

Blue nevus is a common melanocytic neoplasm, whereas blue nevus–like melanoma (BNLM) is uncommon, with most lesions arising in the skin. Here, we present an unusual case of BNLM in the pelvis with no clinically identified cutaneous primary. A 32-year-old female with a history of papillary thyroid carcinoma presented to her gynecologist for abdominal pain and dyspareunia for two years.  Ultrasound and CT scan demonstrated a large mass adjacent to the uterus in the midline pelvis measuring up to 10 cm. No lymphadenopathy or additional mass was detected. Intraoperatively, in addition to the dominant mass, numerous pigment deposits were identified in the abdominal and pelvic peritoneum. Routine histopathology of the resected tumor showed proliferation of atypical heavily pigmented spindled cells with mitoses, necrosis, and calcifications. By immunohistochemistry, the tumor cells were positive for SOX10, pan-melanoma, and p16, and negative for S100. Next-generation sequencing test revealed mutations involving GNA11 and SF3B1 consistent with BNLM. Alterations involving BRAF, NRAS, and PRKAR1A were not detected. Clinical screening for a potential primary in the skin, anorectal region, colon, vulvovaginal tract, and eyes was negative. Patient was treated with immunotherapy (nivolumab and ipilimumab) post-operatively. Five months post-surgery, she is alive with no evidence of tumor recurrence.  Exceptional cases of primary intra-abdominal melanoma arising in association with extracutaneous blue nevus have been reported recently. The current case may represent an additional such case with no residual identifiable precursor blue nevus, although metastasis from regressed cutaneous primary cannot be excluded.