If "cancer" was this new disease that appeared in 2020 and it was highly contagious I'm pretty sure similar measures would have been taken. Or in other words, lockdown doesn't help combat the spread of cancer but it helps against airborne diseases. On the other hand, we haven't ignored cancer, AFAIK is one of the family of diseases that has most of the research funding going into (at least pre-2020) and it shows, the treatment efficiency for many types of cancer in 2020 is much better than it was 50 years ago.
So then... what's your point?