We took a combinatorial in silico and in vitro approach to identify and verify the isoform switch between 3′-end isoforms of HNRNPA1. We show that HNRNPA1 isoforms with different 3′UTRs have different half-lives and the cancer-specific isoform switch contributes to increased HNRNPA1 protein abundance in breast cancer cells. Here, HNRNPA1 is linked to breast cancer.