Rhabdoid Carcinoma of the Rectum
A 49-year-old Caucasian male presented to the outpatient clinic with symptoms of tenesmus, abdominal pain, blood and mucus in stool, and weight loss of over 40 kg during the previous 6 months. A circular ulcerated and stenosing tumor was discovered on colonoscopy and was located 13 cm above the anal verge. A partial total mesorectal excision (TME) with a resection of the right ureter and urinary bladder (tumor penetrated these structures), as well as dissection of the right lateral pelvic node, was performed; 27 of 51 harvested lymph nodes contained metastases. No distant metastases or other tumors were discovered at the time of surgery.\nGross examination demonstrated a broadly ulcerated, deeply infiltrative tumor within the rectal wall, measuring 7 cm in greatest dimension, growing through the adventitia into the adjacent urinary bladder that was removed together with a segment of bowel. Microscopically, the lesion was composed of two components: over 99% of it showed a rhabdoid morphology with discohesive solid sheets of pleomorphic epithelioid cells, little stroma and few inflammatory cells in between. Abundant eosinophilic cytoplasm with a large excentric nucleus and a single prominent nucleolus was present in the majority of the tumor cells. Numerous mitotic figures, including atypical forms, were present (). No "signet-ring" cells were identified. The second minor component constituted a poorly-differentiated adenocarcinoma and was present only in one tissue block section located at the periphery of the main tumor mass just underneath the intact colonic mucosa (). It was composed of irregular, cribriform glands lined by large atypical cells with prominent nucleoli and scant cytoplasm, surrounded by a desmoplastic inflammatory stroma.\nLymphovascular invasion was present. Metastatic disease was identified in multiple mesenteric lymph nodes and constituted a spread of pure rhabdoid cells without an adenocarcinoma component. Assessments of the surgical resection margins raised the possibility of microscopic residual disease.\nRhabdoid cells demonstrated positivity for pancytokeratin, vimentin, and epithelial membrane antigen, and were nonreactive to cytokeratin 7 (CK7), cytokeratin 20 (CK20), thyroid transcription factor-1, homeobox protein CDX-2 (CDX-2), desmin and myogenic differentiation 1 (MyoD1). The minor adenocarcinoma component vanished on deeper sections; nevertheless, pancytokeratin, vimentin and CDX-2 stains were positive whereas CK7 and CK20 stains were both negative. INI1 antibody stained all neoplastic nuclei within the rhabdoid component (). A microsatellite analysis was undertaken by applying markers to MLH1, MSH2, MSH6, and PMS2 and showed no loss of expression of all 4 of them in tumor cells.\nMutation analysis of the rhabdoid tumor component revealed a wild-type (not mutated) KRAS gene and BRAF V600E mutation.\nRectal lesions are strongly believed to represent a primary neoplasm based on their overall gross appearance and clinical presentation. They are circular, dominant rectal tumor with no other lesions being identified at the initial workup, making metastatic disease in the rectum almost impossible. The immunophenotypic pattern was informative with respect to conclusively confirming the rhabdoid morphology; however, it was not suggestive of organ specificity to help rule out secondary dissemination to the rectum. Identification of a minor adenocarcinoma component was most useful. It strongly argued for the lesion to represent a primary rectal composite rhabdoid tumor. With the rhabdoid morphology in mind, an epithelioid sarcoma was also on the differential list; however, given that both rhabdoid tumors and epithelioid sarcomas share almost identical histological, immunohistochemical and molecular patterns, separation of these two entities may have been impractical and nearly impossible []. Again, the presence of a minor adenocarcinoma component strongly favored a rhabdoid tumor, as it would not be expected to occur in an epithelioid sarcoma.\nA month past surgery, a computed tomography (CT) scan disclosed multiple metastases within abdominal lymph nodes, iliac vessel invasion, and probable disease spread to the liver. Intensive chemotherapy was initiated: 4 cycles according to the chemotherapy regimen, consisting of folinic acid (leucovorin), fluorouracil (5-fluorouracil), and irinotecan (FOLFIRI) regimen were administered. The therapy course was complicated by development of bilateral pneumonia and ascites that were treated with antibiotics and drainage. Three months into the postoperative course, a repeated CT scan demonstrated disease progression despite aggressive chemotherapy. The patient received four additional cycles of chemotherapy according to the chemotherapy regimen, consisting of folinic acid (leucovorin), fluorouracil (5-fluorouracil), and oxaliplatin (FOLFOX4) regimen; however, again, no improvement was observed, metastatic disease rapidly spread to leptomeninges, neurological symptoms developed, and the patient eventually passed away 7 months after initial disease presentation.