Among hereditary cases, almost a fourth result from a mutation in one of a few rare but highly penetrant genes, including breast cancer 1 (BRCA1), breast cancer 2 (BRCA2), phosphatase and tensin homolog (PTEN), tumor protein P53 (TP53), E-cadherin (CDH1) and serine/threonine kinase 11 (STK11), which present up to an 80% lifetime risk of developing breast cancer [4]. The gene discussed is PTEN; the disease is breast carcinoma.