Clear cell adenocarcinoma of the colon arising in endometriosis: a rare variant of primary colonic adenocarcinoma.

Colonic adenocarcinomas composed predominantly or exclusively of cells with clear cytoplasm are extremely rare. 1 2 Considerable diagnostic diYculties can arise in distinguishing primary colonic clear cell adenocarci-noma and metastatic carcinoma from sites such as ovary or kidney. Here, we describe a case of primary colonic clear cell adenocarci-noma that probably arose in endometriosis. The possible presence of endometriosis was only appreciated on review and after the examination of multiple levels and extra histological sections. A 65 year old woman presented with crampy lower abdominal pain and the passage of blood and mucus from the rectum. Barium enema showed an apparently malignant stricture of the rectosigmoid and she underwent an anterior resection. Preopera-tive serum CA125 was not measured. At surgery , the clinical impression was of a primary colorectal tumour. Small haemorrhagic nod-ules were present on the pelvic and abdominal peritoneum, suggestive of endometriosis. There were multiple metastatic lesions within the liver. Both ovaries and kidneys appeared normal. The surgical specimen consisted of a 30 cm length of colon. A polypoid ulcerated tumour involved the mucosa and infiltrated through the full thickness of the colonic wall. Histology of the tumour showed an ulcer-ated surface. The tumour was composed entirely of cells with abundant clear cyto-plasm and prominent cell membranes (fig 1A). Several growth patterns were present. Much of the tumour had a pronounced pap-illary pattern, with hyalinised cores covered by tumour cells (fig 1A). Tubular and solid areas were also identified. There was moderate nuclear pleomorphism and low mitotic activity, with a formal mitotic count revealing 1–2 mitoses/10 high power fields. Areas of necrosis were present and there was extensive lymphovascular permeation, both within the tumour and within submucosal and serosal lymphatics away from the tumour. Calcified psammoma bodies and intracytoplasmic periodic acid SchiV (PAS) positive eosinophilic hyaline inclusions were also present. The adjacent colonic mucosa showed no dysplas-tic features. The tumour infiltrated through the full thickness of the colonic wall into the surrounding fat. Situated within the fat, on the external surface of the tumour, a cystic structure was present. This had an epithelial lining, which focally consisted of a single layer of plump cells with abundant eosinophilic cytoplasm (fig 1B). These cells merged with a single layer of cells with abundant clear cytoplasm, similar to those seen within the main tumour. Surrounding the cyst a fibrous stroma was present but no definite endometrial type stroma was identified. Histology …