Naked Mole Rats are protected from cancer because their tissues are very rich with high molecular weight hyaluronan (HMW-HA).

http://www.sciencedaily.com/releases/2013/06/130619132444.htm

Previous research by Seluanov and Gorbunova showed that the p16 gene in naked mole rats stopped the proliferation of cells when too many of them crowd together. In their latest work, the two biologists identified HMW-HA as the chemical that activates the anti-cancer response of the p16 gene.