As the article says, this immunotherapy essentially works by turning off some of the immune system's "don't attack your own body" safeties. This frees the immune system to attack the cancer (provided it can identify it).
One big advantage of immunotherapy is that the therapy causes a long-term (permanent? I'm not sure anyone knows; the drugs are less than a decade old) change to the immune system - the body continues to attack the cancer even after the drug treatment has ceased.
If you put these two things together, however, you might see why the side effects can be so bizarre. Your immune system might decide that the liver looked at it funny one day, but then decide that the GI tract is actually the real troublemaker a few days later. And since the immune system change persists post-treatment, so do the side effects.
These side effects can (usually) be controlled with corticosteroids (hydrocortisone/prednisone/etc.), which have an immunosuppressant effect. Of course, long-term corticosteroid use has its own severe side effects (plus severe dependency issues). And if you're suppressing the immune system, then you're suppressing the mechanism that the immunotherapy uses to fight the cancer in the first place. The treatment and the side effects are two sides of the same coin.
> this immunotherapy essentially works by turning off some of the immune system's "don't attack your own body" safeties
That sounds like checkpoint inhibitor immunotherapy. Others like CAR-T may have fewer side effects, since they're just augmenting your T cells with a manufactured supply that is primed to attack a specific target.
CAR-T is a lot more expensive for now but over time such "precision" immunotherapies may become mass produced and cheaper and we'll be able to make the immune system do what we want with fewer side effects.
My buddy had bad GI symptoms(throwing up, diarrhea). He also lost his adrenals and thyroid. His thyroid may come back, but he'll be on pills for the rest of his life. IIRC, the treatment lasted about 2 years. He had the advantage of being a guitarist by trade who lived at home anyway. I'm not sure how someone with a normal life would have made it through it. He was the only patient who made it all the way through the trial. He also smoked cigarettes and marijuana, and had a opioid habit. That said, he still managed to keep hiking a couple times a week except on his roughest chemo weeks.
Even if you don’t, it can cause such a condition. My immune system “boosted” itself into erathyma multiforme during a nasty cold and that particular issue persisted for years even after the cold was long gone.
Our immune systems are fantastically complicated, probably more complex a defense system than the entire US military with hundreds of millions of years of evolutionary pressure.
