I think the tricky nuance with determining what has caused someone’s cancer is that cancer emerges after a few pre-cancerous mutations rather than just the one - kind of like a slippery slope mutation cascade that increases the likelihood of full blown malignant cancer by massive amounts with each mutation. So whilst smoking might cause one of those mutations, it’ll take a few more to become malignant! And then another few more to become metastatic cancer, the biggest killer