These folks would live forever except, according to the article, they’re all accident-prone alcoholics. So maybe the gene that keeps them cancer free also makes them accident-prone alcoholics instead?
Maybe being a dwarf in the boondocks is a risk factor for hitting the sauce or accidents when using adult sized tools?.
From the abstract linked in comment# 1:
A possible explanation for the very low incidence of cancer was suggested by in vitro studies: Serum from subjects with GHR deficiency reduced DNA breaks but increased apoptosis in human mammary epithelial cells treated with hydrogen peroxide.
It is an assumption that the growth hormone receptor mutation is the only abnormality. Something in their serum either repairs damaged DNA or tells the cell to die, i.e. apoptosis, aka programmed cell death. This is just the beginning of the story, IMHO. One treatment for all of the different cancers has been oncology's Holy Grail.