Rhabdoid carcinoma of the rectum

Abstract

Rhabdoid colonic tumors are very rare lesions with just a few publications describing such neoplasms. Even more unusual for these lesions are their primary rectal locations, with only two brief case reports having been published on that subject to date. We present a case of a composite rhabdoid rectal carcinoma in a 49-year-old male. The tumor behaved very aggressively, with rapid patient demise despite radical surgery and intensive postoperative chemotherapy (FOLFIRI [folinic acid {leucovorin}, fluorouracil {5-fluorouracil}, and irinotecan] and FOLFOX4 [folinic acid {leucovorin}, fluorouraci {5-fluorouracil}, and oxaliplatin]). Pathologic examination was supportive of a rhabdoid carcinoma, with a compatible immunohistochemical profile, demonstrating synchronous expression of vimentin and epithelial markers in the tumor cells. In addition, BRAF V600E gene mutation, together with a wild-type KRAS gene, was identified, and no evidence of microsatellite instability based on MLH1, MSH2, MSH6, and PMS2 immunophenotypes, i.e., no loss of expression for all 4 markers, was observed. Our reported case confirms previously published observations of the clinical aggressiveness and the poor therapeutic response for rhabdoid tumors.

Keywords: BRAF; Carcinoma; INI1; Rectum; Rhabdoid tumor.

Fig. 1

High-power view of malignant rhabdoid cells showing abundant eccentric eosinophilic cytoplasm, large nuclei with prominent nucleoli and numerous mitotic figures. Scant stroma and few inflammatory cells in between.

Fig. 2

Medium-power view of both tumor components: rhabdoid cells are infiltrating the muscularis propria. Note the small clusters of irregular, cribriform glands (arrowheads), infiltrating the lamina propria.

Fig. 3

High-power view of the INI1 immunohistochemical stain. Note the strong and uniform nuclear positivity in the rhabdoid tumor cells.