KLK3 and prostate cancer: Another shared antigen, TARP21, expressed in about 95% of prostate cancers of all Gleason types and about 50% of breast cancers, has shown promise as a peptide vaccine in HLA-A*0201+ patients with stage D0 prostate cancer by reducing the tumor growth rate as measured by prostate-specific antigen (PSA) slope in about 74% of vaccinated patients at 1 year22.