Among the 21 Rasal1‐Pten double‐KO mice, 42.9% (9/21) developed hyperplasia (6 in thyroid gland and 3 in both thyroid gland and uterus) and 57.1% (12/21) developed cancers, including 11 thyroid cancer and 1 lymphoma. This evidence concerns the gene RASAL1 and hyperplasia.