Anorectal
Anal Canal Adenocarcinoma
Anal canal adenocarcinoma is a very rare type of cancer that arises from the glandular cells within the anal canal, distinct from the more common squamous cell cancer.
Reviewed by Allen Kamrava, MD, MBA, FACS, FASCRS · Last reviewed 2025-10-12
Overview
What is anal canal adenocarcinoma?
Anal canal adenocarcinoma is a very rare form of anal cancer. Unlike the most common type of anal cancer, which is squamous cell carcinoma arising from the skin-like cells of the anus, adenocarcinoma arises from the glandular cells. These glandular cells are found in the upper part of the anal canal near the rectum or within the anal glands that are located in the wall of the anal canal. Because of its rarity and its similarity to rectal cancer, it can be a diagnostic and therapeutic challenge. It can sometimes arise from a long-standing perianal fistula, particularly in patients with Crohn's disease.
Symptoms
What are the symptoms?
The symptoms of anal adenocarcinoma are often non-specific and can be similar to other anorectal conditions, including the more common squamous cell carcinoma. Symptoms may include:
- Rectal bleeding
- Anal pain or discomfort
- A palpable mass or lump in the anal canal
- Mucus discharge
- A change in bowel habits
- Persistent, non-healing wound or fistula
Causes & risk factors
What causes anal canal adenocarcinoma?
The exact cause is often unknown. Unlike squamous cell carcinoma of the anus, which is strongly linked to the human papillomavirus (HPV), the role of HPV in anal adenocarcinoma is not well established. It is thought to arise from the glandular tissue of the upper anal canal or from the submucosal anal glands. Chronic inflammation is believed to be a significant risk factor. It has been known to develop in the setting of:
- Chronic anal fistulas
- Long-standing Crohn's disease
- Prior pelvic radiation
When to see a doctor
When should I see a doctor?
You should see a doctor if you have any persistent anorectal symptoms, especially bleeding, pain, or a palpable mass. If you have a history of a chronic, non-healing anal fistula that has persistent drainage or develops a hard, lumpy area, it is very important to seek evaluation to rule out a malignancy. Early diagnosis is key to successful treatment.
Urgent — get care now
When is it an emergency?
Anal adenocarcinoma is not typically an acute emergency. However, if the tumor causes a complete blockage of the anal canal leading to an inability to pass stool or gas, or if there is heavy, uncontrolled bleeding, you should seek immediate medical attention.
Diagnosis & tests
How is it diagnosed?
Diagnosing anal adenocarcinoma requires a high index of suspicion due to its rarity. The diagnosis is confirmed by a biopsy.
- Physical Examination: A digital rectal exam and anoscopy are performed to evaluate the tumor's size, location, and fixation to surrounding structures like the sphincter muscles.
- Biopsy: A tissue sample is taken from the suspicious area and examined by a pathologist.
- Staging: Once the diagnosis is confirmed, staging is performed to determine the extent of the cancer. This is crucial for planning treatment and is done similarly to rectal cancer:
- Pelvic MRI or Endorectal Ultrasound (ERUS): To assess the depth of tumor invasion and involvement of nearby lymph nodes.
- CT Scan of the chest, abdomen, and pelvis to look for distant spread (metastases).
Treatment
How is anal canal adenocarcinoma treated?
Because it is so rare, there is no single standard of care, and treatment is often modeled after the treatment for low rectal adenocarcinoma. Treatment decisions are usually made by a multidisciplinary team.
- Surgery: The primary treatment is typically surgery. Because the tumor involves the anal canal and sphincter muscles, the most common operation is an Abdominoperineal Resection (APR). This involves removing the anus, rectum, and a portion of the sigmoid colon, and results in a permanent colostomy.
- Neoadjuvant Therapy: For larger or more advanced tumors, a combination of chemotherapy and radiation therapy is often given before surgery (neoadjuvant therapy), similar to the approach for locally advanced rectal cancer. This can help shrink the tumor and increase the chances of a successful surgical removal.
- Local Excision: For very small, early-stage tumors that do not involve the sphincter muscles, a local excision may be considered in highly selected cases, but this is uncommon.
- Chemotherapy for Advanced Disease: For cancer that has spread to distant organs, chemotherapy is the main treatment.
Frequently asked questions
Is this the same as rectal cancer?
While it is treated very similarly to a low rectal adenocarcinoma, a true anal canal adenocarcinoma is distinct because it arises from the glands within the anal canal itself, rather than the lining of the rectum. This distinction can be important for staging, as anal canal tumors can spread to the inguinal (groin) lymph nodes, which is rare for rectal cancer.
What is the prognosis?
The prognosis for anal adenocarcinoma is generally considered to be poorer than for both anal squamous cell carcinoma and rectal adenocarcinoma. This is often because the diagnosis is made at a more advanced stage. However, with aggressive, multimodality treatment, long-term survival is possible.
References
- Sands DR, Mahmoud NN. Anal Cancer. In: Steele SR, Hull TL, Hyman N, Maykel JA, Read TE, Whitlow CB, eds. The ASCRS Textbook of Colon and Rectal Surgery. 4th ed. Springer; 2022:365-366.
- National Cancer Institute. Anal Cancer Treatment (PDQ®)–Patient Version. Published March 18, 2022. Accessed October 12, 2025. https://www.cancer.gov/types/anal/patient/anal-treatment-pdq
- Hill, M., Tak-Yin, T., & Brown, C. J. (2018). Adenocarcinoma of the Anal Canal: A Systematic Review. Diseases of the Colon & Rectum, 61(10), 1214–1222.