Theory: A supposition or an assumption based on certain evidence or observations but LACKING SCIENTIFIC PROOF (emphasis added).
[Source: Taber's Cyclopedic Medical Dictionary]

We can agree to disagree. While there is much known, particularly in the area of causal relationships, the actual mechanisms for causing cancer still remain a mystery and are shrouded in theories and hypothesis, some of them conflicting.
These theories form the basis upon which treatment protocols are developed. The "viral causes" are also a theory.

I have yet to see a "doctrine" or "principle" associated with cancer, which would be the next step up from a theory.

Do a google search on "Oncogene Theory" - I rest my case (and read just the ones from accredited institutions not the oddball ones).

The original question that I responded too was "Anyone know of any other reasons I may have got this?" Just to keep the thread on topic.

I do agree with you on one thing - the reason ISN'T as important as the cure and good health habits.