Cellular mutations for many of the cancers are unique. In those cancers they can indeed tell you what began the mutation that led to that particular cancer. Leukemia would be one of these. I'm not sure what the point of your posting is. If you expose yourself to three known risk factors, that are well documented as the primary causes of the disease (90%+), you would like to state that it is likely that you came from some unknown source?

I will agree that there are no absolutes in cancer. But wanting to believe that you were biologically unique enough to not have what happened to millions before you, happen to you, and blame it on some esoteric other possibility, serves what purpose? Since you can't go back and change things, (nor change your genetic make up) this seems like a mental exercise that has few benefits other than rationalization. As cancer survivors, I would think that we have gotten a taste of the big picture enough that this kind of thing is no longer important to us. But you are right, in some instances people will never know which, of the may possible combinations of things, brought them to a specific place. But we certainly have a good understanding of why the vast majority of people come to this disease. Having said that, nothing in life is absolute... except perhaps that it will eventually end.