This is a big question for those in the field of cancer immunotherapy, treatment based upon the concept of adjusting the immune system to reject and destroy tumors.
The National Cancer Institute along with a company called NewLink Genetics are looking to get FDA approval to start clinical trials of a drug that restricts a natural mechanism for immune suppression.
This enzyme named IDO, has been shown to help the fetus avoid rejection by the mother's immune system. This discovery led scientists to suspect and later prove that tumors express IDO.
Will suppressing IDO in humans help the immune system to seek out and kill cancer cells? This is what these scientists want to find out.
Doctor Mellor, a pediatric oncologist, says "What (cancers) do, we think, is make a protective cocoon so the immune system does not attack the tumor, so that gives you the therapeutic opportunity. If you stop IDO from blocking the response, you should allow the response, so now the specificity of the immune system is brought to bear directly on tumor cells"
Interesting stuff!
Way back in my sun worshipping days -- when I longed for a golden tan, logged countless hours scorching my body, and ignored my grandma's warnings that my pale skin was just not tough enough for the sun's powerful rays -- I would have basked in joy over headlines now surfacing in the media. They go something like this: the sun may actually fight skin cancer instead of causing it. 
