My friend who's wife was going thru chemo said that's what it's like. Instead of trying other less harmful methods first. His quote was "you're not only killing the cancer, but everything else as well and the hope is the cancer dies before other stuff." His wife did pull thru and is OK for now, but the quality of life during the process was bad.
Cancer isn't just a "thing" you can treat. It invades one of more of your tissues -- liver, pancreas, lungs, breasts, brain, lymph nodes, stomach, colon, ... it's an equal opportunity disease that's glad to spread itself wherever it can.
Chemo isn't just a more harmful method. It's most often the only method left to stop cancer that's gone beyond a certain stage of migration. By treating the entire body, you hopefully remove the cancer cells which allows healthy cells to regenerate and replace them. That does take time, but unless it's caught early and able to be removed surgically in a limited area, chemo can either stop the cancer completely or at least slow it down enough to give you more time on Earth.
Whether that time is something you'd welcome given the agony you may be in is another topic.