I think its fair to say that nobody really fully understands cancer.
If somebody did then we would have a cure by now.
Clearly we know there is a connection between some things and cancer.
Sun exposure and skin cancer, smoking and various cancers, alcohol and various cancers, HPV which is sexually transmitted and cervical and oral cancer.
And I totally agree we should adopt behaviours to try and avoid those cancers.
But sometimes cancer is just fucken random or genetic or whatever.
My little brother died of leukemia/blood cancer.
He was a beautiful boy and I miss him every day of my life.
My uncle was a crazy cool dude and died of lung cancer and he never smoked a cigarette in his life.
Shit happens.