I don't think I believe that myself. If expectorant effects helped prevent cancer, then people who took lots of expectorant medicines--or even people who coughed a lot from bronchitis, for instance--would have lower rates of cancer. And that's not the case.

It appears to be the anti-inflammatory/anti-carcinogenic properties in THC and how it works at the cellular level. In lab-rat studies, THC has amazing anti-cancer effects on certain types of cancer cells and causes unique and beneficial types of cell-pruning. This is what Tashkin and the other researchers theorize is happening, and I expect they're right.