Contagious Cancer

The common wisdom is that one can't "catch" cancer from another person.  While this may be true for most cancers there are probably exceptions. One interesting case involves a type of cancer in dogs called Sticker's sarcoma.  This cancer spreads from dog to dog during sex and when dogs byte or lick each other.

One fascinating point from the discovery published in the journal Cell is that the tumor is probably hundreds of years old (compare to the everage dog lifespan of 13 years)! The tumor is essentially immortal as it jumps from one animal to another.

"Robert A. Weinberg, a pioneer in the genetic underpinnings of cancer at the Whitehead Institute for Biomedical Research in Cambridge, Mass., said he was not surprised to learn that genetic studies had confirmed that Sticker's is a transmissible cancer, given the strength of earlier clues. But he agreed that the phenomenon raises difficult questions about why more cancers do not spread this way."
http://www.washingtonpost.com/wp-dyn/content/article/2006/08/10/AR2006081001535.html

Cell. 2006 Aug 11;126(3):477-87.
Clonal origin and evolution of a transmissible cancer.
Murgia C, Pritchard JK, Kim SY, Fassati A, Weiss RA.
MRC/UCL Centre for Medical Molecular Virology, Division of Infection and Immunity, University College London, 46 Cleveland Street, London W1T 4JF, UK.
Abstract
The transmissible agent causing canine transmissible venereal tumor (CTVT) is thought to be the tumor cell itself. To test this hypothesis, we analyzed genetic markers including major histocompatibility (MHC) genes, microsatellites, and mitochondrial DNA (mtDNA) in naturally occurring tumors and matched blood samples. In each case, the tumor is genetically distinct from its host. Moreover, tumors collected from 40 dogs in 5 continents are derived from a single neoplastic clone that has diverged into two subclades. Phylogenetic analyses indicate that CTVT most likely originated from a wolf or an East Asian breed of dog between 200 and 2500 years ago. Although CTVT is highly aneuploid, it has a remarkably stable genotype. During progressive growth, CTVT downmodulates MHC antigen expression. Our findings have implications for understanding genome instability in cancer, natural transplantation of allografts, and the capacity of a somatic cell to evolve into a transmissible parasite.