mosaic cancer predisposition by PPM1D, the etiology is genetic, but not hereditary

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3759028/

PPM1D is Wild-type p53-induced phosphatase 1, gene dose upregulation was reported in breast and ovarian cancers. This study involving a team of nearly 400 collaborators, showed germline PPM1D cancer causing mutations are mosaic, with gain of function (equivalent to dose upregulation), and the mutant allele is lost in the tumour. Intriguing twists.