Can immunotherapy cause bleeding and how to manage it

Immunotherapy can sometimes be associated with bleeding, although it is not among the most common side effects. ^[1] Certain immunotherapy drugs, including some monoclonal antibodies and immune checkpoint inhibitors (like pembrolizumab), list various bleeding events in their official safety information. ^{[2] [3]} In many cases, bleeding happens indirectly for example, from inflammation of the gut (colitis) causing bloody stools or from low platelets due to immune-related effects so early recognition and prompt management are important. ^{[4] [5]}

Why bleeding can occur

• Immune activation against normal tissues: Checkpoint inhibitors can trigger inflammation in organs such as the colon (colitis), which may lead to blood in the stool or black, tarry stools. ^[4]
• Drug-specific risks: Some monoclonal antibodies carry a risk of internal bleeding. ^[2]
• Listed adverse events: Official prescribing information for pembrolizumab includes a wide range of hemorrhagic events (for example, gastrointestinal bleeding, nosebleeds, hematuria, hematemesis, subdural hematoma), indicating bleeding has been observed across different body systems. ^{[3] [6]}

Warning signs to watch for

• Blood in bowel movements or black, tarry stools, which can signal intestinal bleeding. ^[4]
• Easy bruising or bleeding in unusual places (gums, nosebleeds) or tea-colored urine that may reflect blood or organ involvement. ^[4]
• Persistent or heavy bleeding from cuts, nosebleeds that do not stop within recommended time frames, or periods heavier than usual. ^{[7] [8] [9]}

What to do right away

• For a nosebleed: Sit up, lean forward, pinch the soft part of your nose, and apply ice; seek help if it does not stop after about 30 minutes. ^[8]
• For a cut: Apply firm pressure with gauze and use ice; contact your team if bleeding does not stop after about 10 minutes or is very heavy. ^[9]
• If you notice blood in stool, black/tarry stools, vomiting blood, coughing blood, blood in urine, sudden severe headache, or unusual bruising, contact your care team urgently, as these can be signs of significant bleeding. ^{[7] [4]}

Day-to-day measures to reduce bleeding risk

• Be gentle with oral care to reduce gum bleeding; consider a soft toothbrush and alcohol-free mouth rinses, especially if you have mouth sores. ^[10]
• Avoid activities or products that raise bleeding risk, such as drinking alcohol and using enemas, rectal suppositories, or vaginal douches; avoid tampons if periods are heavier than normal. ^[9]
• Protect skin from cuts and bruises; use an electric razor and be cautious with sharp objects. ^[7]

Managing immune-related causes

Bleeding can stem from immune-related adverse events that affect the gut (colitis) or blood components (for example, immune thrombocytopenia). ^{[4] [5]} These reactions may escalate quickly, so early reporting and close monitoring by your oncology team are essential, and they often improve with timely immunosuppressive therapy when indicated. ^[5] In some situations, your oncology team may pause immunotherapy until symptoms stabilize. ^[11]

When to seek urgent care

• Heavy or persistent bleeding anywhere on the body. ^[7]
• Black, tarry stools, or bright red blood in stool. ^[4]
• Vomiting blood or coffee-ground–like material. ^[6]
• Severe headache, weakness, confusion, or sudden neurologic changes that could suggest internal bleeding. ^[12]
• Blood in urine or tea-colored urine. ^[4]

If any of these occur, contact your oncology team or seek emergency care immediately. ^[7]

Key takeaways

• Bleeding can occur with immunotherapy and may be a sign of organ inflammation or a drug-related effect. ^{[1] [2]}
• Recognize early signs (bloody or black stools, unusual bruising, persistent nosebleeds) and act promptly. ^{[4] [8]}
• Practical steps pressure on cuts, correct nosebleed technique, avoiding irritants can help while you arrange medical review. ^{[9] [8]}
• Close communication with your care team and, when needed, temporary treatment holds or specific therapies can reduce risk and complications. ^{[11] [5]}