Composite intestinal adenoma-microcarcinoid in the colon and rectum: a case series and historical review

Abstract

Background: Composite intestinal adenoma-microcarcinoid (CIAM) is a rare colorectal lesion that mostly comprises a conventional adenomatous component with a minute proportion of neuroendocrine (NE) component. Although microcarcinoids are well-recognized in the setting of chronic inflammatory disorders of the gastrointestinal tract, large intestinal microcarcinoids associated with intestinal adenoma are exceedingly rare and their clinicopathologic characteristics are yet to be elucidated. This study was performed to clarify their clinicopathologic characteristics and to review the relevant literature.

Methods: In total, 24 cases of CIAM in which tumors were excised endoscopically (n = 22) or surgically (n = 2) were retrieved from the Department of Pathology, Daehang Hospital. We analyzed their clinicopathologic characteristics and performed immunohistochemical staining for NE markers to determine their endocrine nature.

Results: CIAM usually developed in middle-aged and elderly patients, with a mean age of 62.0 years (range, 44-81 years). Thirteen patients were men and 11 were women, indicating a nearly equal sex ratio. Unlike classic carcinoid tumors, CIAMs occurred mostly in the colon (83.3% of cases), particularly in the proximal colon. Histologically, the microcarcinoid component consisted of low-grade NE cells arranged in small nests, glands or cords interspersed with glandular elements or less frequently resembled squamous morules. There was no expansile nodular or organoid growth pattern, which is typical of carcinoid tumors. The microcarcinoids were 1-20 mm in size (mean size, 4.7 mm) and were mostly situated in the basal lamina propria with no submucosal layer involvement; none showed desmoplastic reaction or increased proliferative activity. Follow-up data (mean, 23.1 months) were available for 18 patients; all patients are alive and well.

Conclusions: To the best of our knowledge, ours is the largest series of patients with CIAM in the English-language literature. Microcarcinoids found in CIAMs appear to show favorable clinical outcomes regardless of their size, likely due to the absence of submucosal extension and/or increased proliferative activity. We recommend avoiding additional radical surgeries in patients who have endoscopically undergone complete CIAM excision unless they exhibit ominous histologic features such as submucosal extension or increased proliferative activity.

Keywords: Colorectal lesions; Composite intestinal adenoma; Microcarcinoid; Neuroendocrine tumor.

Fig. 1

Histological and immunohistochemical findings of composite intestinal adenoma-microcarcinoid. a Low power magnification shows adenomatous polyp with hardly recognizable microcarcinoid component (×40). Black arrows indicate microcarcinoid component. b High power magnification displays adenomatous glands and neuroendocrine cell nests in the lamina propria, which are connected to each other (×200). c Immunohistochemical staining for synaptophysin shows diffuse cytoplasmic reactivity in the microcarcinoid component (×200). d The microcarcinoid component is diffusely stained for chromogranin-A on immunostaining (×200)

Fig. 2

Histological and immunohistochemical features of composite intestinal adenoma-microcarcinoid, mimicking invasive carcinoma. a Low power magnification shows adenomatous glands with minute microcarcinoid component (black arrows, ×40). Arrow heads indicate adjacent carcinomatous area. b High power magnification reveals endocrine cell nests with angulated shape and infiltrative growth pattern, harboring the potential for misdiagnosis as carcinoma invasion (×200). c Immunohistochemical staining for synaptophysin shows diffuse cytoplasmic reactivity in microcarcinoid component (×200). d The microcarcinoid component displays focal positivity for chromogranin-A on immunostaining (×200)

Fig. 3

Histological and immunohistochemical features of composite intestinal adenoma-microcarcinoid, mimicking adenoma with squamous metaplasia (squamous morules). a Low power magnification shows adenomatous glands with a few eosinophilic cell nests (black arrows) in basal lamina propria (×40). b High power magnification shows adenomatous glands and eosinophilic cell nests resembling squamous metaplasia (×200). c Immunohistochemical staining for synaptophysin shows diffuse cytoplasmic reactivity in the eosinophilic cells nests, supporting the neuroendocrine differentiation (×200). d The neuroendocrine component is negative for chromogranin-A on immunostaining (×200)