irAEs: What They Are, Why They Matter, and How They Affect Your Treatment

When you start immunotherapy for cancer, your immune system gets turned up to fight tumors—but sometimes, it turns on your own body. These unintended attacks are called irAEs, immune-related adverse events that occur when the immune system mistakenly targets healthy tissues. Also known as immune-mediated adverse reactions, irAEs can show up weeks or months after treatment begins, and they’re not rare. About half of people on checkpoint inhibitors like pembrolizumab or nivolumab will experience at least one. Unlike chemo side effects, which hit fast and hard, irAEs creep in quietly. A rash here, fatigue there, a cough that won’t quit—these might seem minor, but they’re red flags.

irAEs aren’t one thing. They’re a whole family of reactions, each tied to different organs. Checkpoint inhibitors, drugs like Keytruda and Opdivo that release the brakes on immune cells are the main culprits. They work by blocking proteins like PD-1 or CTLA-4, which normally keep immune responses in check. Take those brakes off, and your T-cells go wild—not just at cancer, but at your skin, gut, liver, lungs, even your thyroid or pituitary gland. That’s why you see irAEs in the skin, rashes and itching are the most common, affecting up to 40% of patients, or the gastrointestinal tract, where diarrhea and colitis can become life-threatening if ignored. The liver gets hit too—elevated enzymes aren’t just a lab curiosity, they’re a signal to pause treatment. And don’t forget the endocrine system: thyroid problems and adrenal insufficiency from irAEs are often permanent, requiring lifelong hormone replacement.

What makes irAEs tricky is how unpredictable they are. Two people on the same drug, same dose, same cancer type—maybe one gets a mild rash, the other ends up in the hospital with pneumonia. That’s why early detection matters more than anything. If you’re on immunotherapy, you need to know the warning signs: persistent diarrhea, new joint pain, shortness of breath, yellowing skin, or unexplained mood swings. These aren’t "just side effects"—they’re your body screaming for help. And the good news? Most irAEs can be managed if caught early. Steroids, dose delays, or switching drugs can stop the damage before it becomes permanent.

The posts below dive into real-world cases, treatment adjustments, and what doctors actually do when irAEs show up. You’ll find stories from people who had to pause immunotherapy for a rash, others who needed emergency steroids for colitis, and insights on how to talk to your oncologist when something feels off. This isn’t theoretical—it’s the lived experience of thousands on immunotherapy right now. Whether you’re a patient, caregiver, or just trying to understand what’s happening, these articles give you the facts you need to act fast, stay safe, and not let fear silence your voice.