Composite intestinal adenoma-microcarcinoid: An update and literature review

Figure 1 Composite intestinal adenoma-microcarcinoid consisting of tubulovillous adenoma with high grade dysplasia and microcarcinoid components (arrowheads) at its base. A: The overall polyp architecture is preserved (Hematoxylin and eosin, 50 ×); B: Microcarcinoid component shows bland cytology, within edematous stroma with conspicuous eosinophils, resembling desmoplasia (Hematoxylin and eosin, 200 ×).

Figure 2 Composite intestinal adenoma-microcarcinoid with submucosal invasion of the microcarcinoid component. A: The microcarcinoid (MC) components (arrowheads) form small nests that are sparsely distributed at the polyp base. No nodules or masses are grossly evident (Hematoxylin and eosin, 100 ×); B-D: The MC components are positive for synaptophysin and beta-catenin (nuclear stain) with low proliferative rate (arrowheads) (B: Synaptophysin immunostain, 100 ×; C: Beta-catenin immunostain, 100 ×; D: Ki 67 immunostain, 100 ×).

Figure 3 Squamous morules (arrows) with associated tubulovillous adenoma (Hematoxylin and eosin, 100 ×).

Figure 4 Composite intestinal adenoma-microcarcinoid with associated squamous morules (arrows). Both microcarcinoid (arrowheads) and squamous morules (arrows) show low proliferative rate and positivity for CK5/6 and beta-catenin (nuclear staining), suggestive of a shared pathogenesis. A: Hematoxylin and eosin, 100 ×; B: Ki 67 immunostain, 100 ×; C: CK5/6 immunostain, 100 ×; D: Beta-catenin immunostain, 100 ×.

Figure 5 Microcarcinoid component of composite intestinal adenoma-microcarcinoid may mimic invasive adenocarcinoma. A: The microcarcinoid component is found at the base of full-thickness adenomatous glands (Hematoxylin and eosin, 100 ×); B: However, the constituting cells are positive for synaptophysin immunostain (Hematoxylin and eosin, 100 ×).

Figure 6 Rectal neuroendocrine tumor forming a nodule/polyp. A: The epicenter of the tumor is in the submucosa and the tumor extends to the deep margin (Hematoxylin and eosin, 40 ×); B: High magnification view shows typical trabecular growth pattern (Hematoxylin and eosin, 200 ×).

Figure 7 Appendiceal goblet cell adenocarcinoma. A: The tumor nests infiltrate and undermine the appendiceal mucosa (Hematoxylin and eosin, 50 ×); B: Bland cytology may mimic well-differentiated neuroendocrine tumor such as seen in the microcarcinoid component of composite intestinal adenoma-microcarcinoid (Hematoxylin and eosin, 200 ×).

Figure 8 Mixed neuroendocrine-non-neuroendocrine neoplasm. A: Mixed colonic adenocarcinoma (upper right) and large cell neuroendocrine carcinoma (lower left); B: Mixed colonic squamous cell carcinoma and large cell neuroendocrine carcinoma (Inset: high magnification view shows squamous differentiation). Hematoxylin and eosin, 100 ×.