Elephants have a very low rate of cancer; and humans have an approximately 40% chance of developing cancer. Why? One explanation is humans have one copy of the P-53 tumor suppressor gene, and elephants have 20 copies of the P-53 gene.  Immortal pathogens can be the originating root cause of cancer, and can also damage the functioning of the P-53 gene. Damage to the P-53 gene reduces the ability of the immune system to suppress cancer cells, and provides an environment to support of chlamydial growth.

Cell Rep.2014 Nov 6;9(3):918-29. doi: 10.1016/j.celrep.2014.10.004. Epub 2014 Oct 30.