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Rectal Cancer Treatment (PDQ®)

Health Professional Version

Cellular Classification and Pathology of Rectal Cancer

Adenocarcinomas account for the vast majority of rectal tumors in the United States. Other histologic types account for an estimated 2% to 5% of colorectal tumors.[1]

The World Health Organization classification of tumors of the colon and rectum includes the following:[2]

Epithelial Tumors


  • Tubular.
  • Villous.
  • Tubulovillous.
  • Serrated.


  • Adenocarcinoma.
  • Mucinous adenocarcinoma.
  • Signet-ring cell carcinoma.
  • Small cell carcinoma.
  • Adenosquamous carcinoma.
  • Medullary carcinoma.
  • Undifferentiated carcinoma.

Carcinoid (well-differentiated neuroendocrine neoplasm)

  • Enterochromaffin-cell, serotonin-producing neoplasm.
  • L-cell, glucagon-like peptide and pancreatic polypeptide/peptide YY–producing tumor.
  • Others.

Intraepithelial neoplasia (dysplasia) associated with chronic inflammatory diseases

  • Low-grade glandular intraepithelial neoplasia.
  • High-grade glandular intraepithelial neoplasia.

Mixed carcinoma-adenocarcinoma

  • Others.

Nonepithelial Tumors

Malignant lymphomas

  • Marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue type.
  • Mantle cell lymphoma.
  • Diffuse large B-cell lymphoma.
  • Burkitt lymphoma.
  • Burkitt-like/atypical Burkitt lymphoma.

(Refer to the PDQ summary on Adult Non-Hodgkin Lymphoma Treatment for more information.)


  1. Kang H, O'Connell JB, Leonardi MJ, et al.: Rare tumors of the colon and rectum: a national review. Int J Colorectal Dis 22 (2): 183-9, 2007. [PUBMED Abstract]
  2. Hamilton SR, Aaltonen LA: Pathology and Genetics of Tumours of the Digestive System. Lyon, France: International Agency for Research on Cancer, 2000.
  • Updated: January 26, 2015