In honor of 420 (marijuana legalization day is April 20th and hipster code for the drug is “420”) we cite an article experimenting on mice liver cancer.
They suggested that treatment with cannabinoids decreases TERT (telomerase) expression and therefore inhibits hepatic carcinoma.
http://www.sciencedirect.com/science/article/pii/S209050681400027X
This is not to say that marijuana causes cancer but that perhaps an existing cancer cannot survive as efficiently in its presence. For clarification of this point, see this blog posting.