When I first got here 80% of oral cancer was caused by environmental factors such as tobacco products and/or excessive alcohol use - that has been supplanted by the HPV virus (which is now the dominate cause, and hence why so many younger people are now coming here) and there are tests for that. EBV has also been closely watched as a causitive factor.

Once you have cancer it is more academic - whether HPV or environmentally induced the treatment modalities are the same.

OC can be caused by many other things as well, virtually anything that irritates the oral tissues on a regular basis, which might explain the small percentage of unknown etiology.

The immune system plays a roll and genetic propensity may also factor in to some degree.