Sorry haven't got much time at the moment, here's the paper that got me interested

Anti-tumoral action of cannabinoids: Involvement of sustained ceramide accumulation and extracellular signal-regulated kinase activation

http://www.nature.com/nm/journal/v6/n3/abs/nm0300_313.html

Put that into Google Scholar (the paper title or just "guzman thc"), then click on the Cited by xxx below in the search results to find newer papers.

GW Pharma is a company doing clinical trials, and i think Canadian licenced producers of cannabis are doing trials as well (though i don't know how many are about cancer/anti-tumoral activity).

Here's a long list of research papers on cannabinoids:

http://www.cannabis-med.org/studies/study.php