According to some studies, there is a link between high serum level of vitamin D and low cancer incidence. Here for example:
http://www.ncbi.nlm.nih.gov/pubmed/19523595
Researchers from McGill University may have found why:
http://www.mcgill.ca/newsroom/channels/news/newly-discovered-effects-vitamin-d-cancer-219089
According to this article, they claim "we discovered that vitamin D controls both the rate of production and the degradation of cMYC. More importantly, we found that vitamin D strongly stimulates the production of a natural antagonist of cMYC called MXD1, essentially shutting down cMYC function".
Interestingly, in synovial sarcoma, nuclear accumulation of cMYC is significantly associated with a higher rate of relapse: