In the present study, we provide evidence that KDM5B, a H3K4 demethylase, may exhibit two contrasting functions: in human PCa, it is significantly upregulated (consistent with an earlier report; 27) and correlates with poor patient survival thus pointing to an oncogenic role; in contrast, genetic deletion of Kdm5b leads to mild hyperplasia in the mouse prostate, pointing to a potentially tumor-suppressive function. The gene discussed is KDM5B; the disease is neoplasm.