Oncogenic protein dosage is tightly regulated to enable cancer formation but how this is regulated by translational control remains unknown. The Myc oncogene is a paradigm of an exquisitely regulated oncogene and a driver of pancreatic ductal adenocarcinoma (PDAC). Here we use a CRISPR interference screen in PDAC cells to identify activators of selective MYC translation. The top hit, the RNA-binding protein RBM42, is highly expressed in PDAC and predicts poor survival. We show that RBM42 binds and selectively regulates the translation of MYC and a precise suite of pro-oncogenic transcripts, including JUN and EGFR. Mechanistically, we find that RBM42 binds and remodels the MYC 5' untranslated region structure, facilitating the formation of the translation pre-initiation complex. Importantly, RBM42 is necessary for PDAC tumorigenesis in a Myc-dependent manner in vivo. This work transforms the understanding of the translational code in cancer and illuminates therapeutic openings to target the expression of oncogenes.