Immune-related side effects: early signals and when to report concerns

The first time I heard the phrase “immune-related adverse event,” I pictured a smoke alarm that sometimes rings late and sometimes too loudly. That image stuck, because cancer immunotherapy can nudge the immune system into fighting cancer—and occasionally, it also irritates healthy tissues. I wanted a way to notice the earliest wisps of “smoke,” so I started keeping simple notes: When did the cough begin? Is the rash itchy or painful? Did the fatigue arrive with a low-grade fever or a new headache? Writing it down made the patterns clearer. Over time, I built a short list of cues for myself—what looks like a normal off-day versus what deserves a same-day message or a night-and-weekend call.

The moment this all clicked for me

It was during a routine clinic visit. A nurse asked me to rank my diarrhea from “mild” to “severe.” I realized I didn’t have a shared yardstick. My “mild” could be someone else’s “moderate.” That’s when I learned about grading symptoms and why timing matters. A high-value takeaway from that conversation: even low-grade symptoms can be important in immunotherapy, because catching them early often keeps life calmer—fewer ER visits, fewer interruptions in treatment, and fewer steroids overall. For a concise, clinician-approved overview of how teams think through these toxicities, I found the NCCN immunotherapy toxicity guidance (2025) especially helpful for framing my questions.

  • Write down the first day you noticed a symptom and how it has changed day by day.
  • Note any triggers (new meds, infection exposure, intense activity) and what helps or does not help.
  • Share your baseline (what’s normal for you) so your team can tell what’s truly new.

A simple traffic-light guide I use to sort signals

I’m not a clinician, but I needed an easy way to decide how urgently to speak up. This is the non-alarmist, practical system I landed on—always deferring to my care team’s instructions:

  • Green = monitor and message soon. Mild symptoms that don’t disrupt daily life: faint rash without pain, one or two loose stools above your normal, a dry cough without shortness of breath, mild fatigue, or a slightly tender thyroid area with normal energy. Send a portal message within 24–48 hours and keep a log.
  • Amber = call your team within 24 hours. Symptoms that are new, persistent, or spreading: rash covering larger areas or with blisters, three or more loose stools above baseline, new shortness of breath on stairs, chest tightness that comes and goes, headache that wakes you up at night, light sensitivity, eye pain, jaundice (yellowing skin/eyes), dark urine, or fasting blood sugars running high if you normally have none. Call the clinic; your team may want labs or imaging. See the NCI’s patient page for how different organs can be involved.
  • Red = urgent care now. Severe chest pain, severe or rapidly worsening shortness of breath, fainting, confusion, seizures, severe abdominal pain with blood in stool, severe headache with neck stiffness, muscle weakness that affects walking or lifting arms, markedly decreased urine, vision changes, or fevers that don’t respond to antipyretics. If you can’t reach your oncology team quickly, seek emergency care. Teams use guideline-based pathways—like ASCO/ESMO/NCCN—to triage these safely and then decide whether to hold immunotherapy or start medicines that calm the immune system.

If you like references as much as I do, here are a few that shaped this “traffic light” mindset:

Early patterns I watch by organ system

Immune-related side effects (often called irAEs) can show up in almost any organ. The timing varies—some happen in the first 6–12 weeks, others months later, and some even after treatment ends. That’s why I pay attention to small shifts. Here are the early “tells” I try not to ignore, using plain language first and the medical term in parentheses:

  • Skin (dermatologic): new itchy patches, hives, tender redness, or blistering; rare but serious peeling or widespread painful rash needs urgent attention.
  • Gut (colitis): more frequent, looser stools; cramping; blood or mucus; belly pain that doesn’t match typical food-related upsets.
  • Lungs (pneumonitis): dry cough plus new shortness of breath, especially if stairs or light activity suddenly feel harder.
  • Hormones (endocrinopathies: thyroid, adrenal, pituitary, pancreas): unexplained fatigue, cold intolerance, hair shedding, headaches behind the eyes, dizziness on standing, salt cravings, nausea, or new high blood sugars.
  • Liver (hepatitis): more nausea than usual, poor appetite, right-sided upper abdominal ache, dark urine, or yellowing eyes/skin.
  • Joints and muscles (rheumatologic/myositis): stiff hands, morning joint swelling, muscle pain or weakness that makes climbing stairs or rising from a chair difficult.
  • Nerves (neurologic): new severe headache, facial droop, trouble swallowing, double vision, numbness/tingling that climbs, or weakness that seems to spread.
  • Heart (myocarditis/pericarditis/arrhythmia): chest pain, rapid or irregular heartbeat, fainting, or severe shortness of breath at rest—these are red by default.
  • Kidneys (nephritis): swelling in legs, markedly less urine, or new flank pain.
  • Eyes (uveitis): eye pain, new floaters, light sensitivity, or blurred vision.

Most of these have a range—from mild and manageable to severe and urgent. Clinicians grade them using common criteria and then decide whether to continue, hold, or stop therapy and whether to start medicines like corticosteroids or other immunomodulators. The key for me: don’t wait for perfect certainty to reach out. A short note early is better than a long apology late.

How I prepare before each infusion

I keep a one-page “symptom snapshot” that fits in my bag and mirrors what my team asks at visits. It speeds up the conversation and helps the whole team see trends quickly. Here’s what’s on it:

  • At-a-glance timeline: first day of any new symptom, when it got better or worse, and what changed around that time.
  • What I tried: rest, fluids, OTC meds (only those cleared by my team), warm compresses, skin moisturizers, etc.
  • Numbers that matter: temperature, home blood pressure or blood glucose (if relevant), weight changes, and any home oxygen readings if I have them.
  • Medication list: dose, timing, and any new prescriptions or supplements since last visit.
  • Questions for today: “If X returns, what should I do?” “If the clinic is closed, who do I call?”

For a patient-friendly primer (and a good checklist to print), the NCI immunotherapy side-effect guide is clear and grounded. Professional societies like ASCO and ESMO publish more technical guidance for clinicians that still helped me understand the “why” behind decisions.

My three-step way to decide what to do next

I lean on a compact “Notice–Compare–Confirm” loop:

  • Step 1 — Notice: Is this symptom new, changed, or clearly different from my usual?
  • Step 2 — Compare: How many times a day? How intense? Is it spreading, and is it interfering with sleep, walking, eating, or work?
  • Step 3 — Confirm: Check my clinic’s instructions and send a message or call. If I can’t reach them and the symptom sounds “red,” I seek urgent care and make sure to say I’m on immunotherapy.

Clinicians often distinguish between mild (monitor), moderate (call and likely adjust/hold), and severe (urgent evaluation). That mindset is consistent across major guidelines (for example, ASCO and ESMO) even though the exact steps are tailored to each organ system.

Little habits that helped me stay ahead of trouble

  • Skin first aid: fragrance-free moisturizers after showers, sunscreen daily, and loose clothing. If a rash appears, I snap a photo each day to show progression.
  • Hydration and electrolytes: boring but potent for early diarrhea. I ask before using OTC anti-diarrheals; sometimes they’re fine for mild symptoms, sometimes the team wants labs first.
  • Sleep and temperature logs: a cheap thermometer and three lines in a notes app tell a surprisingly rich story when fatigue or fever creeps in.
  • Staying vaccine- and infection-aware: I separately ask about timing and type of vaccines and how to handle sick contacts while on therapy.
  • Clear after-hours plan: I keep the on-call number on the fridge and in my phone favorites.

It also helped me to know that health systems track and report immune-related adverse reactions in very structured ways (for example, see the FDA guidance on how immune-mediated events are characterized for new cancer immunotherapeutics). That might sound dry, but it’s reassuring: your report becomes part of a larger safety net. If you’re curious, the document is here: FDA guidance on immune-mediated reactions (2022).

What makes me call right away

When in doubt, I err on the side of a quick call. Here’s my personal “no debate” list because these can progress fast without help:

  • Breathing changes: shortness of breath, chest pain, or a rapidly escalating cough.
  • Neurologic alarms: confusion, fainting, sudden weakness, severe headache with neck stiffness, or trouble seeing.
  • GI red flags: severe abdominal pain, persistent vomiting, or blood in stool.
  • Cardiac concerns: new palpitations, dizziness with exertion, or swelling plus shortness of breath.
  • Signs of adrenal crisis: profound fatigue with dizziness on standing, nausea, and low blood pressure—especially if I’m tapering steroids.

In those moments, I let the ER know I’m on immunotherapy so they can loop in oncology and use relevant pathways quickly.

Conversations I practice before I need them

It’s easier to talk about thresholds on a calm day than in a midnight panic. I’ve asked my team:

  • “Which symptoms mean hold therapy until labs come back?”
  • “If I develop diarrhea at 2 a.m., should I take anything before calling?”
  • “What does a safe steroid taper look like if I ever need one?” (I don’t start or stop steroids on my own.)
  • “Do you want photos of my rash or a daily log?”
  • “If I travel, what’s the backup plan for urgent care that knows immunotherapy?”

What I’m keeping and what I’m letting go

I’m keeping three principles on the fridge door:

  • Notice early, speak early — small symptoms matter here.
  • Use shared language — mild/moderate/severe with concrete examples helps everyone.
  • Team sport, not solo — decisions about holding therapy or using medicines to calm the immune system are not DIY.

And I’m letting go of the idea that reporting a symptom is “complaining.” It’s actually part of good treatment. If you like to read more deeply, the clinician playbooks below are trustworthy and consistent across continents.

FAQ

1) How soon can immune-related side effects show up?
They can appear within weeks of starting treatment, but some happen months later—even after stopping therapy. That’s why teams watch patterns over time. See the ESMO guideline for timing ranges by organ system.

2) Do mild side effects mean my immunotherapy is working?
Not necessarily. Some studies have noted correlations between low-grade side effects and outcomes in specific cancers, but this is not a reliable rule. Treat each symptom on its own merits and follow your team’s plan.

3) Can side effects pop up after treatment ends?
Yes. “Delayed” or “late-onset” events are recognized. Keep your oncology team informed about new symptoms even months after the last dose. The NCCN guidance specifically calls out late presentations.

4) Should I use over-the-counter meds for diarrhea or rash before calling?
Sometimes yes for mild symptoms—but ask first. Teams often want a basic lab check to rule out infection or to monitor electrolytes and liver function, and they’ll advise which OTC options fit your situation.

5) Who do I contact after hours or on weekends?
Most cancer centers have an on-call clinician for immunotherapy patients. Store the number in your phone and on your fridge. If you have red symptoms and cannot reach the team, seek emergency care and state you’re on immunotherapy.

Sources & References

This blog is a personal journal and for general information only. It is not a substitute for professional medical advice, diagnosis, or treatment, and it does not create a doctor–patient relationship. Always seek the advice of a licensed clinician for questions about your health. If you may be experiencing an emergency, call your local emergency number immediately (e.g., 911 [US], 119).