Have you heard of the Tasmanian Devil? It is the largest surviving carnivorous marsupial in the world found exclusively in Tasmania. In the mid 90s, a plumber named Christo Baars from Holland, started photographing these animals in Tasmania as a hobby. However by spring 1996 he noticed a decline in their population. He also noticed that the animals had large ugly lumps all over their faces. Soon scientists found regions in which over 90 per cent of the Devils had been wiped out.
These large lumps were ghastly tumours that eventually killed the Devils in large numbers. People guessed the tumours were cause by toxic chemicals or some kind of virus. However neither was found amongst the animals or their habitat. Dr. Anne-Marie Pearse, who was studying the tumour samples from 11 Tasmanian Devils, noticed that the chromosomes from the tumours were completely mangled in the exact same way in each of the 11 samples. All 11 tumours were identical at a genetic level, as though they all came from the same source.
The Devils had “caught” the same type of cancer. But you can’t catch cancer! So how was the same cancer jumping from one animal to another? Cancer is a phenomenon by which cells cannot stop multiplying. Tumours consist of millions of these cells all replicating and competing for space and resources to survive. During this race, every so often there is a replication-error and a cancer cell acquires a mutation. If it’s an advantageous mutation like multiplying or absorbing food faster, these new mutant cells take over. But further replication only leads to more mutations until eventually the cancer cells secrete a substance called matrix metalloproteinases which allows the cells to dissolve out of the primary tumour site, enter the blood stream, adhere to a new site and grow there. Based on what we know about cancer and the Tasmanian Devils, these curious jumping tumours have been explained by the fact that Tasmanian Devils are always attacking each other and biting each other on their faces. So it easy to imagine how a tumour from one Devil’s face might crumble into the wound of another and grow there. Sadly for the Devils, their immune system is not robust due to the inbreeding of the species allowing for these cancers to easily flourish in their new host.
On a final note of adapting tumours, similar to the case of the Tasmanian Devils, the canine transmissible venereal tumour has been evolving for up to 2500 years! It is the oldest continuous animal tumour cell line known to man. But when a tumour lives that long it has become a living parasite and not a mere tumour cell anymore. This is evolution and adaptation at its best.
The writer is a Ph.D. in Molecular Genetics and Genomics and is working on skin cancer at Novartis