Can Mesothelioma Cause Blood in the Stool?

Blood in the stool is not among the most common first symptoms of mesothelioma, but it can occur in certain situations related to the disease or its treatment. Pleural mesothelioma typically presents with chest symptoms, while peritoneal mesothelioma (in the abdomen) can cause abdominal pain, swelling, and bowel changes like constipation or diarrhea; frank gastrointestinal bleeding is less typical but has been reported. ^[1] Peritoneal cancer spread within the abdomen can also lead to rectal or vaginal bleeding, especially when tumor deposits involve or press on parts of the gastrointestinal tract. ^[2]

Importantly, blood in the stool can also result from treatment complications, such as chemotherapy‑related bleeding risks, and from unrelated but common gastrointestinal conditions (like hemorrhoids or ulcers) that occur in anyone, including those with cancer. ^{[3] [4]}

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What “Blood in the Stool” Looks Like

• Bright red blood coating the stool or on toilet paper suggests lower GI bleeding (often the colon or rectum). ^[5]
• Black, tarry stools (melena) suggest bleeding from higher up in the GI tract, such as the stomach or upper small intestine. ^[5]

If you notice either bright red or black, tarry stools during mesothelioma treatment, it is considered a warning sign that should prompt urgent medical assessment. Unusual bleeding, including red or tarry stools, warrants immediate contact with your care team or emergency evaluation. ^{[3] [6]}

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How Mesothelioma Could Lead to GI Bleeding

Several mechanisms may explain blood in the stool in people with mesothelioma:

1. Tumor Involvement of the Bowel
   Although rare, mesothelioma (pleural or peritoneal) can metastasize to the gastrointestinal tract and form lesions that bleed into the bowel. Case reports document colonic polyps and small‑bowel lesions from metastatic mesothelioma that caused anemia and bleeding. ^{[7] [8]}
   Peritoneal mesothelioma spreads across the peritoneum (the lining of the abdomen) and can wrap around or press on intestines, occasionally leading to bowel changes and, in some instances, bleeding. ^{[9] [2]}

2. Hemorrhage within the Abdomen
   Peritoneal mesothelioma can rarely cause bleeding within the abdominal cavity, and when lesions erode or ulcerate, blood may pass through the GI tract and present as black stools. ^[10]

3. Treatment‑Related Bleeding Risks

   • Chemotherapy regimens used for mesothelioma (such as carboplatin or cisplatin with pemetrexed, sometimes with bevacizumab) can lower platelets or alter clotting, increasing bleeding risk. Patients are specifically instructed to seek urgent care for unusual bleeding or black/tarry stools during these treatments. ^{[3] [6]}
   • Bevacizumab (an anti‑angiogenic drug) is known to increase bleeding risk in some contexts, which is why bleeding warnings accompany regimens that include it. ^{[3] [6]}

4. Common GI Conditions Unrelated to Mesothelioma
   People with mesothelioma can still develop common causes of GI bleeding such as hemorrhoids, anal fissures, peptic ulcers, diverticulosis, inflammatory bowel disease, or angiodysplasia. In cancer populations, a substantial portion of GI bleeds arise from benign lesions rather than the tumor itself. ^{[4] [11]}

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Typical Mesothelioma Symptoms vs. GI Bleeding

• Pleural mesothelioma usually causes chest pain, shortness of breath, coughing, fatigue, and weight loss. ^{[1] [12]}
• Peritoneal mesothelioma commonly causes abdominal pain, swelling, nausea, fatigue, and changes in bowel habits (constipation or diarrhea). ^{[1] [13]}
• GI bleeding is not a hallmark symptom, but it can occur due to bowel involvement or treatment effects and must be evaluated promptly. ^{[2] [3]}

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When to Seek Urgent Care

• Bright red blood in stools or black, tarry stools during or after mesothelioma treatment should prompt immediate medical evaluation, especially if accompanied by dizziness, weakness, or abdominal pain. These are listed as urgent warning signs in standard treatment guidance. ^{[3] [6]}

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How Doctors Evaluate Blood in the Stool

• History and Exam: Clarify color (red vs. black), associated pain, medications (especially blood thinners or NSAIDs), and treatment timeline. ^[5]
• Lab Tests: Hemoglobin/hematocrit to assess for anemia and platelet counts if on chemotherapy. ^{[3] [6]}
• Endoscopy: Colonoscopy for bright red blood and upper endoscopy (EGD) for black stools, which are the cornerstone tests to locate and treat bleeding sources in cancer patients. ^{[14] [15]}
• Imaging: CT scans if bowel obstruction, perforation, or intra‑abdominal lesions are suspected. ^[9]

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Common Causes of GI Bleeding to Consider

Below is a simplified overview of frequent causes and how they relate to someone with mesothelioma:

• Hemorrhoids or Anal Fissures: Bright red blood; common and often benign. ^[4]
• Peptic Ulcers or Gastritis: Black, tarry stools; may be worsened by medications. ^[16]
• Diverticulosis/Diverticular Bleeding: Painless bright red bleeding; common in older adults. ^[17]
• Inflammatory Bowel Disease or Infectious Colitis: Bleeding with diarrhea and abdominal pain. ^[17]
• Angiodysplasia: Recurrent, sometimes occult bleeding; more common with age. ^[17]
• GI Malignancy (colon, stomach, esophagus): Bleeding may indicate a primary GI cancer; requires endoscopic evaluation. ^[14]
• Mesothelioma Metastasis to GI Tract (rare): Reported cases of bleeding colonic or small‑bowel lesions. ^{[7] [8]}
• Treatment‑Related Bleeding (chemotherapy/anti‑angiogenics): Mucosal bleeding, low platelets, or fragile vessels increase risk. Urgent reporting is advised. ^{[3] [6]}

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What to Do If You Notice Blood in Your Stool

• Do not delay: contact your oncology team immediately or go to the emergency department, particularly if stools are black/tarry, if bleeding is heavy, or if you feel faint. These are flagged as urgent symptoms during mesothelioma therapy. ^{[3] [6]}
• Keep a record: note stool color, amount of blood, associated symptoms (pain, dizziness), recent medications (including aspirin/NSAIDs), and timing relative to infusions. ^[5]
• Expect evaluation: you may need blood tests, endoscopy, and medication adjustments; treating the underlying cause often resolves bleeding. ^{[14] [15]}

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Bottom Line

• Yes, blood in the stool can occur in people with mesothelioma, but it is not a classic initial symptom. It most often reflects common GI conditions, treatment‑related bleeding risks, or, more rarely, direct tumor involvement of the bowel. ^{[1] [3]}
• Any new GI bleeding in the context of mesothelioma warrants prompt medical evaluation to rule out serious causes and manage potential treatment‑related complications. ^{[6] [14]}