Sections show a malignant epithelioid neoplasm infiltrating the anterior abdominal wall, composed predominantly of solid sheets and irregular nests of atypical cells within a fibrous stroma. The tumor cells exhibit marked nuclear pleomorphism, hyperchromatic nuclei, and moderate eosinophilic cytoplasm. Mitotic figures are increased. The deeply seated infiltrative growth pattern, in the absence of epidermal involvement, in the appropriate midline infra-umbilical location, raises the possibility of a poorly differentiated urachal carcinoma. However, in view of the predominantly solid architecture composed of cohesive sheets and irregular cellular aggregates, together with the absence of unequivocal gland formation, the differential diagnosis remains broad. Considerations include a high-grade urothelial carcinoma arising from the bladder dome or urachal remnant, secondary involvement by a poorly differentiated metastatic carcinoma (most notably from gastrointestinal, pancreatic, pulmonary, or prostatic primaries), epithelioid variants of primary soft-tissue sarcoma, hematolymphoid neoplasms such as diffuse large B-cell lymphoma, amelanotic melanoma, as well as extragonadal germ cell tumors occurring in midline locations. Definitive classification therefore requires careful integration of radiologic findings, clinical data, and targeted immunohistochemically studies. (CK, CK7, CK20, CDX2, GATA-3, PAX-8, ER, Beta-catenin, Synaptophysin, SATB2, LCA, SALL4).
Lower abdominal swelling below umbilicus.
Soft tissue fragments collectively measured 9.5x8x3, with the largest measuring 5x3.5x3 cm.
Lower abdominal swelling, biopsy: