Often referred to as conventional (traditional) adenoma along with tubular adenoma and villous adenoma, tubulovillous adenoma is a pre-cancerous, neoplastic lesion of the gastrointestinal tract. Often arise in context of biallelic APC gene mutation on chromosome 5, it can also be seen in context of familial adenomatous polyposis. Other risk factors include age, gender, race as well as obesity, sedentary lifestyle, diet, and medications (NSAIDs). Increased number, size and complexity are all associated with increased risk of colorectal adenocarcinoma development.

Macroscopic appearance can be variable from sessile to polypoid and can be hyperemic compared to background mucosa when seen in endoscopy. Microscopically, tubulovillous adenoma contain both tubular (straight/branched crypts) as well as villous (finger-like projections of lamina propria lined by epithelium) components, where each compose 25-75% of polyp volume. Cytologic features include, crowded/pseudostratified elongated nuclei with hyperchromasia, cytoplasmic eosinophilia and loss/decreased goblet cells.

Presence of high grade dysplasia (based on architectural complexity including cribriform/fused crypts, along with loss of polarity, increased mitotic activity further up along the crypt and necrotic luminal debris) and/or intramucosal carcinoma (breach of basement membrane without involvement of muscularis mucosae) must be carefully evaluated.