HOXB13 and pure red-cell aplasia: Prostate cancer (PrCa) is the most commonly diagnosed and second most deadly cancer in men in the US, with over 160,000 estimated new cases and over 29,000 deaths in 2018.[1] There is a substantial genetic component to risk of PrCa, with heritability estimates as high as 58%.[2] Variants in several genes have been associated with increased risk, including HOXB13, BRCA2, BRCA1, ATM, CHEK2, and the mismatch repair genes; however, these occur in only a small fraction of cases and explaining the remaining heritability of PrCa remains elusive.[3–11]