Can a Chronic, Untreated Anal Fistula Cause Cancer?

It is completely natural to worry about cancer, especially if you have had an anal fistula that has gone untreated for a long time. The short answer is: yes, it is possible, but it is extremely rare.

When an anal fistula is left alone for many years—often a decade or more—the constant, long-term inflammation can cause the cells lining the fistula tract to change. In very rare cases, these changes can eventually lead to certain types of cancer, such as mucinous adenocarcinoma or squamous cell carcinoma ^[1][2][3].

How Does This Happen?

Cancer does not develop overnight. The cases reported in medical literature generally involve patients who have lived with an untreated, chronic fistula for anywhere from four to over ten years ^[4][5][6].

Over time, chronic inflammation damages the tissues in and around the anal canal. The ongoing cycle of injury and healing in the fistula tract creates an environment where cells might start to grow abnormally.

Patients with Crohn’s disease or other types of Inflammatory Bowel Disease (IBD) should be especially proactive. Because Crohn’s disease causes persistent, long-term inflammation in the digestive tract, people with this condition have a higher risk of their chronic fistulas developing into cancer ^[7][8]. If you have Crohn’s, it is vital to work closely with a gastroenterologist and a colorectal surgeon to monitor and manage any perianal symptoms ^[3].

When to Seek an Evaluation

One of the main challenges with these very rare cancers is that their symptoms are almost identical to those of a regular anal fistula. A standard, benign fistula will often cause:

• Pain or swelling in the perianal area
• Normal drainage of pus or small amounts of blood

Because these signs are common, cancer can be easily missed if the fistula is not evaluated by a doctor ^[9][10]. However, a sudden change in your symptoms is a strong signal to seek immediate medical care. Warning signs include:

• A new, persistent discharge of jelly-like mucus (which is different from standard pus)
• A new firm lump or sudden hardening of the tissue near the anus
• A significant increase in pain or bleeding

What to Expect at the Doctor

If you have been avoiding the doctor out of fear, embarrassment, or anxiety about what the appointment will involve, you are not alone. Doctors who specialize in these conditions—specifically colorectal surgeons or proctologists—see and treat fistulas every day.

A standard medical evaluation will start with a physical exam. Your doctor may also order imaging, such as a pelvic MRI or an ultrasound, to clearly see the entire fistula tract and rule out any unusual changes ^[11][12].

The good news is that treating your anal fistula effectively prevents this rare complication. Getting your fistula treated—through surgical treatment to close or remove the tract—stops the cycle of chronic inflammation. The type of surgery will depend on how complex your fistula is, but addressing it eliminates the environment where these abnormal cell changes occur. During surgery, your doctor can also take a biopsy (a small tissue sample) and send it to pathology to ensure there are no signs of cancer.