Tubular adenomas are those in which the adenoma cells retain a tubular form similar to that seen in normal colonic mucosa.

• Tubular adenomas are composed of straight or branched tubules of dysplastic tissue; villous adenomas contain finger-like projections of dysplastic epithelium
  • approximately 70% of polyps removed at colonoscopy are adenomas
    • from 70% to 85% of these are classified as tubular (0-25%, villous tissue), 10-25% are tubulovillous (25-75%, villous tissue), and <5% are villous adenomas (75%-100%, villous tissue)

Morphologically they may either be small and pedunculated or sessile lesions.

In general, this type of adenomatous polyp has the least potential for malignant change. The exception is when tubular adenomas occur as part of familial polyposis coli.

Notes:

• most colorectal cancers arise from neoplastic adenomatous polyps (adenomas)
  • adenomas are monoclonal derivatives of a mutated epithelial stem cell. Simple small (<1 cm) tubular adenomas are extremely common and have a low risk of becoming malignant. Only a few acquire the additional genetic alterations that make them grow, develop advanced histological features, and turn to cancer. Advanced adenomas are those that are larger (>1 cm) or that contain appreciable villous tissue or high-grade dysplasia
  • generally accepted that most (>95%) colorectal cancers arise from benign, neoplastic adenomatous polyps (adenomas). Although this adenoma-carcinoma sequence can probably never be proved directly, persuasive data exist indicating that colorectal neoplasia progresses through a continuous process from normal mucosa, to benign adenoma, to carcinoma
    
• some degree of dysplasia exists in all adenomas
  • high-grade dysplasia includes the histological changes previously called 'carcinoma in situ, 'intramucosal carcinoma,' or 'focal carcinoma.'
  • approximately 5-7% of patients with adenomas have high-grade dysplasia, and 3-5% have invasive carcinoma at the time of diagnosis
  • increasing dysplasia and, presumably, malignant potential correlate with
    • increasing adenoma size
    • villous component
    • and patient age
  • likelihood of invasive carcinoma also increases with increasing polyp size