In BRCA-negative families, a greater extent of BC is caused by high to intermediate penetrance of BC genes that explain the genetic predisposition to BC, including several syndrome-predisposing genes: TP53 (OMIM 113721) (Li–Fraumeni syndrome; OMIM 151623), PTEN (OMIM 601728) (Cowden’s disease; OMIM 158350), STK11 (OMIM 602216) (Peutz–Jeghers syndrome OMIM 175200), NF1 (OMIM 613113) (neurofibromatosis; OMIM 162200), and CDH1 (OMIM 192090) (hereditary diffuse gastric cancer syndrome “HDGC”; OMIM 137215) [2]. The gene discussed is STK11; the disease is breast cancer.