PTBP1, a member of the heterogenous nuclear ribonucleoprotein family is overexpressed in a number of cancers including glioma (159, 160), ovarian cancer (161), breast cancer (162), and colon adenocarcinoma (130), and promotes the expression of several protein isoforms associated with tumorigenesis including NUMB Ex9in. Here, NUMB is linked to breast cancer.