It's a fair point to raise. I answer that since lifespans have increased, there isn't anything that is killing people before cancer often enough to account for the drop in cancer deaths.
This is true, but it's also possible that the very treatment that supposedly decreases cancer deaths also decreases the "other illnesses" such that the distance between the cancer death and other illness death is constant. In this case, lifespans could increase and still result in other illnesses killing more than cancer in spite of increased life expectancies.
