Multiple Endocrine Neoplasia type 1 (MEN1) syndrome,3, 4, 5, 6 Multiple Endocrine Neoplasia type 4 (MEN4, caused by CDKN1B)7, 8 and Cowden syndrome (PTEN)9 have been associated with both NET and breast cancer in case reports or case series. This evidence concerns the gene CDKN1B and multiple endocrine neoplasia type 1.