Squamous morula formation in colorectal adenoma: Immunohistochemical and molecular analyses

Pseudoinvasion and squamous metaplasia/morules in colorectal adenomatous polyp: a case report and literature review

BACKGROUND

Submucosal pseudoinvasion and squamous metaplasia (SM) are incidental and special morphological findings in colorectal adenomas, and both can mimic invasive carcinoma. The coexistence of these two findings further increases the risk of misdiagnosis, posing a great diagnostic challenge to pathologists. From 1979 to 2022, only 8 cases have been reported, which was extremely rare. In this report, we presented a case of sigmoid colon adenoma accompanied by pseudoinvasion and SM. Additionally, relevant literature was analyzed to summarize the clinical and pathological characteristics.

CASE PRESENTATION

A 51-year-old Chinese male patient presented with fresh blood after defecation. Electronic colonoscopy revealed multiple polyps, which were removed using a snare and subjected to high-frequency electrocoagulation resection. The largest polyp, located in the sigmoid colon, was a thick pedunculated and lobulated polyp with a maximum diameter of 2.8 cm. The surface of the polyp showed slight ruggedness and redness, and it was sent for pathological examination. Grossly, the polyp had a lobulated and slightly rough surface. Microscopically, it showed a tubulovillous adenoma with focal high-grade dysplasia and mucosal muscle hyperplasia. Glandular elements were observed in the submucosal layer, forming a well-defined lobular structure. Some of the glands displayed cystic change, and focal SM could be seen within the adenoma. SM could manifest as discrete solid cell nests of varying sizes or cribriform-morular-like structures. Immunohistochemical staining showed that SM cells were diffusely positive for cytokeratin 5/6 (CK5/6); p40, p63, and cytokeratin 20 (CK20) were negative; while caudal type homeobox 2 (CDX2) was weakly positive. β-catenin showed abnormal nuclear expression, and an extremely low Ki67 proliferation index was observed.

CONCLUSIONS

Coexistence of SM and pseudoinvasion in colorectal adenomas is highly rare. It is more commonly observed in males and tends to occur in the sigmoid colon. It primarily manifests in tubulovillous adenoma and tubular adenoma, with a majority of cases exhibiting a pedicle. Histologically, it is similar to invasive lesions. The cystic dilation of the submucosal glands, hemosiderin deposition, and the presence of a lamina propria around the submucosal glands without adjacent desmoplastic reaction, suggest pseudoinvasion rather than cancer. The bland cytological morphology and Immunohistochemical markers play a crucial role in distinguishing SM from true invasive lesions.

Colonic invasive adenocarcinoma with squamoid morules: A case report

Colorectal adenomas with squamoid morules are rare; however, colorectal adenocarcinomas are even rarer. Herein, we present a case of colorectal adenocarcinoma with squamoid morules arising from the transverse colon. A 60-year-old Japanese man underwent a colonoscopy, and a Type 0-Is polyp was detected in the transverse colon. The endoscopic findings suggested a high possibility of carcinoma invasion into the deep submucosa. However, endoscopic mucosal resection was performed due to the patient's preference. Histopathologically, the tumor cells mostly formed atypical glandular structures corresponding to adenocarcinomas. Solid nests were observed in parts of the tumor, composed of round, small to short spindles. Immunohistochemically, p63 was positive in some areas, CK20 was negative, and the Ki-67 positive cell rate was almost zero, suggesting a squamoid morule. Based on the above findings, colorectal adenocarcinoma with a squamoid morule was diagnosed; only the fifth case was reported worldwide. Squamoid morules should be carefully differentiated from squamous components of adenosquamous carcinomas.

Composite intestinal adenoma-microcarcinoid: An update and literature review

Composite intestinal adenoma-microcarcinoid (CIAM) is a rare intestinal lesion consisting of conventional adenoma and small, well differentiated carcinoid [microcarcinoid (MC)] at its base. The incidence of CIAM is 3.8% in surgically resected colorectal polyps. While its pathogenesis is unknown, studies support the role of Wnt/β-catenin pathway in the tumorigenesis of CIAM. CIAMs have been primarily reported in the colon wherein they present as polyps with well-defined margins, similar to conventional adenomatous polyps. MC is usually found in adenomatous polyps with high-risk features such as large size, villous architecture, or high grade dysplasia. Histologically, the MC component is often multifocal and spans 3.9 to 5.8 millimeters in size. MC is usually confined within the mucosa but occasional CIAM cases with MC extending to the submucosa have been reported. MC of CIAM demonstrates bland cytology and inconspicuous proliferative activity. The lesional cells are positive for synaptophysin and 60% to 100% of cases show nuclear β-catenin positivity. MC poses a diagnostic challenge with its morphologic and immunohistochemical resemblance to both benign and malignant lesions, including squamous morules/metaplasia, adenocarcinoma, squamous cell carcinoma, sporadic neuroendocrine tumor and goblet cell adenocarcinoma. CIAM is an indolent lesion with a favorable outcome. Complete removal by polypectomy is considered curative. Awareness and recognition of this rare entity will help arrive at correct diagnosis and improve patient care. Currently, CIAM is not recognized as a subtype of mixed neuroendocrine-non-neuroendocrine neoplasm by WHO.

Incidental morphological findings in colorectal adenomas

Owing to a sharp increase in the frequency of diagnosis of colorectal adenomas in the current era of population screening, distinctive morphological features are increasingly being observed. These may present diagnostic challenges and cause clinical management issues. Paneth cell metaplasia is a more common occurrence, but the incidence rates of squamous metaplasia, clear cell metaplasia, osseous metaplasia, neuroendocrine differentiation and signet‐ring cell‐like lesion are low, and they can be seen in <1% of colorectal adenomas. Their histomorphological characteristics are quite unique; ancillary studies are not very helpful and often not needed. In this review, we give an overview and describe the potential clinical consequences of such incidental and special morphological findings in colorectal adenomas.

Combined Intestinal Adenomas/Microcarcinoids

The combined colonic adenoma/microcarcinoid tumor is a rare intestinal neoplasm featuring intermingled adenomatous and carcinoid components. A few case reports and small case series have suggested that this entity exhibits an indolent clinical course. Here, we report two cases with these tumors, and describe the morphological features and clinical follow-up. A 61-year-old male and 78-year-old male presented with heme-positive stools at their medical checkups. Colonoscopy revealed masses in the colons; we performed endoscopic mucosal resection. Both lesions featured low-grade adenomas and low-grade neuroendocrine tumors. We diagnosed combined colonic adenomas/microcarcinoids. The clinical courses of both patients were benign at follow-up at 2.5 and 6 years. Awareness of this rare colonic tumor should prevent potential diagnostic pitfalls and may help clarify the natural history of these tumors and their possible relationships with composite glandular/carcinoid tumors.

Incidence of composite intestinal adenoma-microcarcinoid in 158 surgically resected polyps and its association with squamous morule

Composite intestinal adenoma-microcarcinoid (CIAM) is a rare colorectal lesion consisting of adenoma and small well-differentiated neuroendocrine cell clusters at its base. Its incidence is unknown. Benign squamous morule may demonstrate a neuroendocrine phenotype by immunohistochemistry. We investigated the incidence and clinicopathologic features of CIAM in endoscopically unresectable, surgically removed colorectal adenomas and evaluated its association with squamous morule. Archived pathology materials from 158 surgically resected colorectal adenomas were reviewed. 139 (88%) polyps were entirely submitted for microscopic examination. All lymph nodes were negative for adenocarcinoma and neuroendocrine tumor. CIAM was identified in 6 (3.8%) cases. The microcarcinoid (MC) was distributed over a mean of 5.8 mm (range < 1 to 12 mm), and was multifocal in 5 cases. The MC component was positive for synaptophysin in 6, CK5/6 in 4, and β-catenin in 3 cases. Two of 6 (33.3%) CIAM showed concurrent squamous morule, compared to 4.0% (6 of 152) of adenomas without MC (p < 0.05). At the end of the mean follow-up of 53 months, 4 were free of disease and one patient with previous history of pulmonary large cell neuroendocrine carcinoma (NEC) had a recurrence of NEC. One patient died of an unrelated disease. The incidence of CIAM in surgically removed colorectal adenomas is 3.8%, with an indolent clinical course. Frequent co-expression of CK5/6 and β-catenin in MC combined with common co-existence of squamous morule in the same polyp suggests shared pathogenesis of MC in CIAM and squamous morule, likely representing altered Wnt/β-catenin signaling pathway.

Histopathologic Features of Colorectal Adenoma and Adenocarcinoma Developing Within Inflammatory Polyps in Miniature Dachshunds

Biopsy samples of colorectal polyps were collected and examined from 67 Miniature Dachshund dogs (including 35 cases with an additional biopsy). Histopathologic diagnoses of the initial biopsy samples were "inflammatory polyp" in 52 cases (78%), "adenoma" in 10 cases (15%), and "adenocarcinoma" in 5 cases (8%). Eight of 10 cases (80%) diagnosed as adenoma also had inflammatory polyp lesions in the same specimen. A second biopsy was performed in 25 cases (48%) initially diagnosed with inflammatory polyp. Pathologic diagnoses for the second biopsy were inflammatory polyp in 11 cases (44%), adenoma in 9 cases (36%), and adenocarcinoma in 5 cases (20%). The number of beta-catenin-positive nuclei in epithelial cells was significantly higher in adenoma (46%) and adenocarcinoma (75%) as compared with inflammatory polyp (6%). Normal epithelial cells and hyperplastic goblet cells in inflammatory polyps showed homogeneous positive cytoplasmic immunoreactivity for adenomatous polyposis coli (APC) antigen. However, APC expression was decreased in areas of intense nuclear beta-catenin expression in adenoma and adenocarcinoma lesions. Foci of cytokeratin 5/6-positive squamous cell-like neoplastic cells showed intense beta-catenin nuclear expression that was similar to squamous morules described in human colorectal tumors. The results of the present study suggest that the inflammatory polyp in Miniature Dachshunds is a progressive disease that may develop into adenoma and/or adenocarcinoma. In addition, immunohistochemical findings suggest that aberrations of APC and beta-catenin expression may be involved in tumor development within the inflammatory polyp lesions.