Abstract

A 23-year-old HIV-negative male of African descent reported a 6-month history of a left inferolateral buttock nodule. It increased in size over the first 3 months, and he returned to his country for incision and drainage of the lesion. The lesion subsequently rapidly regrew, and the patient was treated with intralesional triamcinolone and oral doxycycline when he returned to the United States two months later. After 3 weeks, the patient underwent an urgent debulking excision, given its continued growth to 11 cm with ulceration, as well as the patient's report of a 9-pound unintentional weight loss.

Histologic sections demonstrated sheets and lobules of atypical round blue cells with significant cytologic atypia. Prominent foci of atypical mitoses and tissue necrosis were present. Tumoral cells stained strongly using MDM2 and vimentin immunohistochemical (IHC) markers. WT1 and CD99 immunostains strongly and diffusely highlighted lesional cells. The following IHC stains were negative in tumor cells: S100, SOX-10, AE1/3, Pan Cytokeratin, SMA, ERG, CD3, CD45, PAX-5, CD138, Desmin, NSE, P63, HHV8, and EBV. Molecular testing was performed and highlighted CIC-DUX4 gene fusion positivity. This combined with positive immunostaining made the diagnosis of a CIC-DUX4 sarcoma (CDS), which is a high-grade undifferentiated round cell sarcoma. The patient’s pathologic stage at diagnosis was stage IIIA (pT2, pN0, cM0, FNCLCC histologic grade: G3). He was initiated on a multi-drug combination treatment consisting of alternating cycles of VAC (cyclophosphamide, doxorubicin, vincristine) and IE (etoposide and ifosfamide) for an anticipated 3 cycles. Localized CIC-rearranged tumors have a 5-year survival of about 50%.