The average difference between chemo and no chemo at all is similarly underwhelming. Read just about any "when doctors die" piece, and it's clear that they rarely eat their own cooking, and with good reason. Given the choice between "death sentence" and "death sentence, with extra pain and suffering, and a fat bill for the family at the end", I think it's an easy choice.
My dad's cancer spread to the lungs so radiation was off, and his kind didn't respond well to any chemo at the time. He then got pneumonia and the docs told us he'd likely have many months left once the pneumonia was treated, but he would most likely have to stay at the hospital until the end.
He decided to ask them to stop the oxygen supply, and passed away peacefully the following day. It hit hard since it came earlier than expected, but I'm very grateful he was allowed to make that choice. I hope I get to make my own choice if the time comes.
There may be some combination of cancer and treatment where progress has been made, but the aggregates are unimpressive, and if oncology were operating in the light, we'd have more numbers and classifications, and fewer glossy brochures filled with vague bulleted lists. I'd have odds instead of marketing adjectives.