KLK3 and breast cancer: Common adverse events for which there is evidence of association with testosterone therapy include erythrocytosis, acne, oiliness of skin, increase in prostate-specific antigen (PSA) and prostate volume, growth of metastatic prostate cancer, and reduced sperm production and fertility.[20] Uncommon adverse events for which there is weak evidence of association with testosterone administration are gynecomastia, male pattern baldness (familial), and growth of breast cancer.[20]