plus,
you can't patent aspirin for anything even if you work out the biochemical mechanism.
Yes, the conclusion about cancer preventive benefit derived from statistical meta-analysis, so nothing was there about a mechanistic study.
This much we know - it's a cox inhibitor, largely cuts off prostaglandins synthesis. Current food supplies are just too rich in precursors for PGs.
Personally, I think safety profile of aspirin is at least one magnitude better than selective cox2 inhibitors.