This doesn't really say what it looks like it says. They don't have an above average risk of dying of cancer. Rather, if they die they are more likely than average to have died of cancer. Which is not exactly surprising given that the medical screenings remove many of those who would die of heart issues. What would be strange is if there wasn't a higher percentage of cancer deaths.
… IF they die?
To illustrate, my numbers are not meant to be accurate. Population at large, 100 red marbles (heart), 80 black marbles (cancer), 80 blue marbles (everything else). Cancer is 80/260 of the total.
Medical checks, you removed 80 of those red marbles. Now you have cancer at 80/180 of the total.
The percentage of cancer went up. Did the total cancer? No.