Tubular adenoma with squamous metaplasia of the sigmoid colon: a case report

Squamous metaplasia within a sigmoid adenoma. A rare feature

Squamous metaplasia occurring within a colorectal polyp is a rare finding, having a reported incidence of approximately 0.44%. The origin of the squamous cells in this type of setting is uncertain (mechanical irritation and chronic inflammation are potential predisposing factors). It has been implied that the significance of squamous metaplasia in colorectal adenomas is that of a preneoplastic lesion for squamous cell and adenosquamous carcinoma, however the evidence to support this statement is scarce. We present a case of a large tubulovillous adenoma located in the sigmoid, with low-grade dysplasia and multiple foci of p16-positive immunoexpression squamous metaplasia in a 54-year-old Caucasian male, presenting with rectal bleeding.

Squamoid morules in the pseudoinvasive foci of colonic polyp morphologically mimic invasive carcinoma

Colorectal adenomas can show focal squamous differentiation or squamoid morules. We describe histologic findings of squamoid morules in the pseudoinvasive foci of colorectal polyps mimicking invasive carcinoma. Five colonic polyps with squamoid morules in the pseudoinvasive foci were collected. Histologic review and immunostains for cytokeratin 5/6, p63, synaptophysin, and chromogranin were performed on cases with squamoid morules. Forty-seven consecutive colorectal polyps with pseudoinvasion, none of which showed squamoid morules by histology review, and their clinicopathologic features were compared with the cases containing squamoid morules. Cases with squamoid morules more frequently occurred in younger patients (P=.047) and were located in right colon (P=.027) than those without squamoid morules. Diagnosis of the polyps included tubular/tubulovillous adenoma with low-grade (with squamoid morules, n=3; versus without squamoid morules, n=29) or high-grade dysplasia (n=2 versus n=15) and sessile serrated adenoma (none versus n=3). Squamoid morules formed nodules protruding into the lumen of glandular structures or partially replaced adenomatous glands without forming a discrete nodule. They also presented as solid nests showing a well-formed morular structure around the bottom of adenomatous glands or myxoinflammatory stroma. Importantly, squamoid morules often formed a pseudocribriform or solid nest sitting in the stroma of pseudoinvasive foci. All cases (n=4) showed cytokeratin 5/6 positivity and p63 negativity in squamoid morules. Three and 1 of 4 cases showed focal positivity for synaptophysin and chromogranin, respectively, in squamoid morules. Squamoid morules in colonic adenomatous polyps can mimic invasive carcinoma when present in the pseudoinvasive foci. Pathologists should be aware of their presence.

Clear cell change in colonic tubular adenoma and corresponding colonic clear cell adenocarcinoma is associated with an altered mucin core protein profile

Clear cell change is seen in <1% of colonic tubular adenomas (TAs) and remains incompletely characterized. Associated adenocarcinomas can also demonstrate a clear cell phenotype. Eleven TAs with at least focal clear cell change with or without associated invasive adenocarcinoma, from 10 patients were studied. The lesions were stained with periodic acid-Schiff (PAS)/PAS-diastase and immunolabeled with antibodies to MUC2, MUC5AC, MUC6, CK7, CK20, and CDX2. Eight of 11 (77%) TAs with clear cell change had focal to extensive high-grade dysplasia. Two were associated with invasive clear cell adenocarcinoma. The adenomas and adenocarcinomas ranged from 0.5 to 3.5 cm. PAS/PAS-diastase stains showed minimal PAS(+) material in the clear cells. On immunohistochemical studies, the clear cells had decreased MUC2 labeling compared with the surrounding conventional adenoma in 9 of 11 (88%) cases, including the 2 clear cell adenocarcinomas. In 3 of the 11 lesions, the background TA showed at least focal MUC5 immunoreactivity, their associated clear cell area had decreased MUC5 labeling in all 3 cases. No immunoreactivity to MUC6 was observed in the background TAs and clear cells in all cases. Compared with background TA, both increased and decreased expression of CK7, CK20 (in quantity), and CDX2 (in intensity) were observed in the clear cells of TAs and adenocarcinomas. One of the clear cell adenocarcinomas was CK20, CK7, CDX2 and the other was CK20, CK7, CDX2-focal positive. Thus, although the clear cells have different MUC protein profiles than the background adenomatous epithelium, invasive clear cell adenocarcinomas retained the typical CK20(+)/CK7(-) profile of conventional adenocarcinomas. Our results indicate that clear cell adenocarcinomas can be primary to the colorectum with identifiable precursors. Awareness of them and their immunoprofile allows distinction from clear cell lesions from other sites.

Colonic Adenoma With Squamous Metaplasia

Squamous metaplasia arising within colon adenomas is a rare occurrence, with a 0.4% incidence noted predominantly in elderly males. A case of squamous metaplasia arising in a tubulovillous adenoma of the cecum, associated with adenocarcinoma, is described. Squamous metaplasia was immunoreactive for beta-catenin, but negative for cytokeratin 20, CDX2, p63, estrogen receptor, progesterone receptor, p16, and human papilloma virus. Squamous differentiation may serve as a precursor lesion for squamous neoplasia of the colorectum.

Adenosquamous carcinoma of the colon--an immunocytochemical and ultrastructural study. Report of two cases and review of the literature

This paper presents two cases of adenosquamous carcinoma of the colon and brings to 39 the total number documented in medical literature. The concurrent glandular and squamous differentiation of the tumor cells was demonstrated by immunocytochemistry and electron microscopy. Evaluation of the biologic characteristics of all the reported cases suggests that malignant squamous elements in colonic carcinomas behave more aggressively than their glandular counterparts. In contradistinction from the pure squamous-cell carcinoma of the colon, adenosquamous carcinoma does not show the same predilection for the right colon.

Primary squamous cell carcinoma of the colon arising in a villous adenoma

The first case of pure squamous cell carcinoma arising in a villous adenoma of the cecum is reported, and the literature of squamous cell carcinoma of the colon is reviewed. The possible origin of this neoplasm in adenomas of the colon, similar to that of adenocarcinoma, is discussed, and the site distributions of adenocarcinoma and squamous cell carcinoma are compared. The distribution of primary colonic squamous cell carcinoma is found to be predominantly right-sided in comparison to adenocarcinoma (p less than 0.05). Although this result does not preclude adenomas as the origin of most squamous cell carcinomas, it suggests the influence of as yet unknown site-asymmetric factors that are different from those for adenocarcinoma.