@bob, chemo doesn't know anything about cancer. One characteristic of cancer cells is that cancer cells reproduce quickly, so chemo attacks all quickly reproducing cells in the body. That's why some people lose their hair: hair follicles reproduce quickly.

Targeted therapy, on the other hand, only attacks its target. For example, Osimertinib (Tagrisso) is a small molecule targeted therapy that attacks cancer cells with an EGFR mutation. As a result, targeted therapy has far fewer side effects (collateral damage) than chemo and is widely regarded as the future of lung cancer treatment.

@abob, I'm glad to hear that your husband is doing better, and that the immunotherapy is effective for him.
Targeted therapies are generally designed to treat specific cancer mutations (ALK, EGFR, RET...). They leave healthy cells alone while blocking the growth of cancerous cells. Targeted therapies are limited in the types of cancer that they can treat and are generally taken as oral pills.
Just like there are many types of lung cancer, there are many types of treatments. Thankfully we have options now. Without those options, many of us wouldn't be here. We, of course, need more research to continue this trend of advancements, but I'm happy to be here today!