We hope to provide the reader with a broad understanding of CARM1 function in both normal physiological and cancer settings, which will also set the stage for how to prioritize those cancer types that would likely respond best to CARM1 targeting, what biomarkers can be used to stratify these treatments, and what we might expect as off-target or side-effects of prolonged CARM1 inhibitor (CARM1i) treatment in cancer patients. The gene discussed is CARM1; the disease is cancer.