OH and I saw what my mother and FIL suffered during their cancer "treatments" and it literally scarred us for life just how cruel it was, not just the side effects of the treatment, but also the inhumane way they were "cared" for in hospital once they were eventually too weak to stand up for themselves.
It's definitely quality over quantity of life. Both had their last few years absolutely blighted by endless hospital appointments, treatments, awful side effects, etc and cancer killed them both in the end anyway, before they regained any kind of "normal" or enjoyable lives despite their "treatments" being regarded as successes!
They'd both have far preferred to have actually "done" things like holidays, days out, enjoying quality time with grandchildren, etc., rather than being tied to endless rounds of hospital appointments for blood tests, x-rays, scans, consultations, treatments, admissions, etc.
OH got diagnosed with incurable but treatable cancer around 8 years ago. It's a kind of blood cancer, so no need for "operations" as such to remove tumours, growths etc. All "treatable" by chemotherapy mostly. He went through the initial course of chemotherapy drugs but the next stage was a stem cell transplant. He looked into it in great detail as to the process, pros and cons (had to do that himself because the oncologist wouldn't got into the detail and made out it was a standard/straightforward procedure) - but there was massive downsides to it, and in the end he refused to have the procedure. It would have been done in 2018 but he'd have been pretty much house bound throughout 2019 due to his entire immune system being zeroised and having to start again to build up immunities etc., which he found out could take at least a couple of years for the most basic of colds etc. In the event, we had 4 foreign holidays in 2019 as he was fit and well enough, so that was 4 holidays we;d not have had otherwise. Then of course covid hit in 2020 and 2021 so he'd not have been able to go abroad anyway due to the risk of catching covid in crowded places like airports and aircraft! Looking back, it was definitely the right decision not to go ahead with the stem cell transplant. They only gave him a "few years" even if he'd had it, which he's by-passed even though he didn't have it, so no guarantee he'd be alive today if he'd gone ahead and died of either complications of the treatment (which happens) or contracting covid or norovirus or something else afterwards due to having no immunity system.
People have to do their own research and make their own decisions. I'd never judge anyone for whatever decision they make when it comes to major surgery and/or chemotherapy etc.