Cancer is genetically linked, that’s how the gene for breast cancer was found in the first place. Most od the research for BC was from the Later Day Saint’s (Mormons?) record books, and was found to be gentically linked on the X chromosome, that’s why women take tests for breast cancer in the first place. Plus it is a known fact that a person has increased chances of cancer if their close relatives have or are suffering from cancer.
Also don’t downplay physcologists dude, sure most mental illnesses can be attributed to not being able to handle stress, but saying “It’s all just weak will” is like saying feeling sick is because your body isn’t strong and doctors only make up diseases to make themselves feel more important.
Not trying to argue, just trying to improve your ideals.