That was my first thought too
My hypothesis is that it might be too early, as in the father didn't have cancer at that point in the past, so a healthcare check up wouldn't give any indication that he would have this disease.
I assume he will take his father either some time soon, or maybe even use his manager's mother's case as a way to persuade his father ti get checked out. Who knows though
It’s also very much of a lifestyle disease, stress, tragedies or lasting difficulties can trigger it. Getting out of a bad job, eating better, resting more , having more happy time could all contribute to him not being affected or in a lesser way
Of course it’s not the only thing, but the body is self healing a lot of cells gone bad, and it can have a significant impact,
There are lots of research on epigenetic, and how lifestyles can dramatically impact health, if you’re interested
wait when he transgressed why didnt he take his father for a health check up or something