Depends on the type of cancer, but some of the new cancer drugs work incredibly fast. My brother got diagnosed with Stage IV lung cancer two years ago but one of the new wonder drugs has mostly dealt with it. “Remission” can be a bit vague, though, and definitely doesn’t mean “cured” - my brother’s wonder drug is known to basically stop working after 2-4 years, at which point he’ll have to switch to a different treatment (and hope that it works as well).