Patients with Cowden syndrome have a high risk for benign and malignant tumors of the breast (lifetime risk – LR-85%), thyroid (LR 35%), kidney (renal cell carcinoma – RCC-, LR 33%), and endometrium (LR 28%), which correspond to sporadic tumor types that commonly exhibit somatic PTEN inactivation (155, 157, 158) (Table 2). This evidence concerns the gene PTEN and Cowden disease.