CDKN1B and breast tumor luminal A or B: However, the advent of massive parallel sequencing that allowed to analyze the cancer genome at very high sensitivity has subverted this notion and indicated that CDKN1B is mutated at a relatively high frequency in prostate cancer (PC) (20), small intestine neuroendocrine tumors (SI-NET) (21) and, especially, in luminal breast cancer (LBC) (22).