Can Immunotherapy Cause Bruising as a Side Effect?

Yes, immunotherapy can sometimes be associated with bruising or bleeding, although this is not among the most common side effects. ^[1] Certain checkpoint inhibitors list easy bruising, petechiae (tiny red or purple spots), and various types of bleeding as potential adverse effects in official prescribing information. ^{[2] [3]}

Why Bruising Can Happen

• Overactive immune response: Immunotherapy can activate the immune system in ways that occasionally affect normal tissues, sometimes including the blood or vessels. ^[4]
• Low platelets (thrombocytopenia): A drop in platelets reduces the blood’s ability to clot, which can show up as easy bruising, nose or gum bleeding, or petechiae. ^[5]
• Drug-specific risks: Checkpoint inhibitors such as pembrolizumab have documented events ranging from injection-site bruising to more serious hemorrhages, though these are uncommon. ^{[2] [3]}

Warning Signs That Need Prompt Attention

• New or worsening bruising, petechiae, or any unexplained bleeding (nose, gums, urine, stool). ^[1]
• Black or tarry stools, vomiting blood, or severe abdominal pain, which can signal bleeding in the gastrointestinal tract. ^[1]
• Sudden severe headache, neurological changes, or vision problems, which can rarely indicate internal bleeding. ^{[2] [3]}

If any of the above occur, contact your care team right away, as early evaluation and treatment help prevent complications. ^[1]

How Your Care Team May Evaluate It

• Blood counts: A complete blood count (CBC) with differential is commonly used to check platelets and other blood cells when bruising or bleeding occurs during immunotherapy. ^[6]
• Additional tests: Depending on symptoms, your team may order other labs (for immune-related blood disorders) and imaging if internal bleeding is suspected. ^[6]

Practical Ways to Cope and Reduce Risk

• Protect your skin: Wear gloves for chores, choose loose, comfortable clothing, and avoid activities with high bruising risk. ^[7]
• Oral care: Use a soft toothbrush and avoid harsh flossing to reduce gum bleeding if your platelets are low. ^[5]
• Medication check: Avoid aspirin, ibuprofen, and other blood-thinning over‑the‑counter pain relievers unless your doctor approves. ^[5]
• Sun safety: If you also have immunotherapy-related skin sensitivity, use SPF 30+ and protective clothing, which can reduce skin irritation that may worsen skin fragility. ^[7]
• Report early: Tell your team promptly about any new bruising or bleeding so they can manage side effects early and safely. ^[1]

Possible Medical Treatments

• Treat the cause: If bruising is due to an immune-related blood effect, your team may adjust immunotherapy or use treatments such as steroids based on severity. ^[6]
• Supportive care: Platelet transfusions may be considered if counts are very low or bleeding is significant, tailored to your individual situation. ^[5]

At-a-Glance: What to Watch For and Do

Situation	What it may mean	What to do
New easy bruising or petechiae	Possible low platelets or vessel irritation	Notify your care team soon. [1] [5]
Nose/gum bleeding, blood in urine or stool	Bleeding from mucosal sites	Call your team promptly. [1]
Black/tarry stools or vomiting blood	Possible GI bleeding	Seek urgent care. [1]
Severe headache or neuro changes	Possible internal bleeding	Seek emergency care. [2] [3]
Using aspirin/NSAIDs without approval	Can worsen bleeding risk	Check with your doctor first. [5]

Bottom Line

• Bruising can occur during immunotherapy, often related to blood or vessel effects, and it deserves attention even if mild at first. ^[1]
• Official drug information for some checkpoint inhibitors includes bruising and various hemorrhages among potential adverse events, though serious bleeding is uncommon. ^{[2] [3]}
• Early reporting, simple protective steps, and appropriate monitoring with blood tests help manage this safely. ^{[6] [1] [5]}