Why does anal cancer cause blood in stool?

Anal cancer can cause blood in stool when abnormal tissue in the anal canal is fragile, irritated, or damaged as stool passes through. The blood may appear bright red on toilet paper, in the toilet, or on the outside of stool. Bleeding can also occur without a bowel movement if the area is inflamed or rubbed.

Blood in Stool is a very common presentation of Anal Cancer. A growth can develop small surface sores or delicate blood vessels, which may bleed with pressure from stool or straining. Bleeding alone cannot identify the cause: piles, anal fissures, bowel inflammation, infections, and other bowel conditions can also cause rectal bleeding. The colour, amount, timing, pain, change in bowel habit, and any lump or discharge can help a clinician decide what examination is needed.

Arrange a medical assessment for new, recurring, or unexplained bleeding. Note whether the blood is on the paper, mixed with stool, or dripping into the toilet, and mention associated itching, pain, a feeling of fullness, mucus, fatigue, or a persistent change in bowel habit. A clinician may ask about medicines that affect bleeding and may examine the anal area and rectum. Avoid assuming the source is piles without an assessment, especially when bleeding continues.

Seek urgent medical care if bleeding is heavy, does not stop, or comes with dizziness, fainting, severe weakness, severe abdominal pain, black tar-like stool, or vomiting blood. Prompt assessment is also appropriate if rectal bleeding is accompanied by an enlarging anal lump, worsening pain, fever, or difficulty passing stool. Even a small amount of blood deserves a timely appointment when it keeps returning.

Ask what examinations could identify the source of bleeding, whether any medicines should be reviewed, and which changes should prompt urgent care. You can also ask whether the bleeding pattern suggests a problem in the anal canal or farther inside the bowel, and how you will receive follow-up results.