I'm about to play the Devil's Advocate. Keep that in mind. :icon_twis
It is quite possible that higher rates of bone cancer, specific to one area, could be initiated secondary to trauma. Because of the repeated blows sustained from heavy bag conditioning, checking kicks, etc etc, the bone is essenetially in a perpetual state of trauma.
So what is the body's response to this? Repair, of course. And being the highly efficient machine that it is, build it stronger; stronger via a denser bone matrix. Now, it is possible that traumatized cells have damaged DNA, and when these cells start to replicate, a form of cancer starts (proven to be the initiating factor in other types of cancer). Keep in mind this is just off the top of my head, and I'm no oncologist.
As added food for thought, why is it that osteogenic sarcoma is prevalant in pedicatrics, specifically ones engaged in athletic activities? I haven't read about the type of cancer proported in Thais, but it would be interesting to find some solid studies.