I'm not talking about the treatment, I'm talking about why he let your dad get cancer to begin with. Why does cancer even exist in the world? Assuming the premises that god is perfect, all-powerful, and benevolent are true, creating/letting cancer to exist in the world goes against each one of those claims. If god purposefully created cancer, he is not benevolent. If god does not have the ability to remove cancer, he is not all-powerful. If god did not purposefully create cancer, he is neither all-powerful nor perfect.