In my experience, most people with cancer that I know simply oscillate between having life-threatening active cancer/tumors and remission.

I don't know any case where people have detectable cancer and it's just being managed, I think that's more the exception than the rule.

For my girlfriend, when she was in her last stages they had to do that (try to slow down/manage the cancer instead of remove it), but that was already palliative care and she died soon after. Also, the only reason they didn't try removing the tumor is because the specific location in the brain (pons) is inoperable.