<prompt> Most common Familial Breast cancer gene:BRCA1BRCA 2Li-Fraumeni syndromeSTK 11  <response>: Ans. a BRCA 1Ref Sabiston 20th Edition 832 Hereditary breast cancer - 5-10 BRCA1 - 45 MC hereditary Breast cancer BRCA2 - 35 P53Lifraumeni - 1 Peutz jeughers, Cowden disease, Muir torre syndrome, Ataxia telangiectasia all less than 1 each. 