Therefore, if a patient on TRT has a PSA level of 4.0 ng/mL or higher, or even if it is less than 4.0 ng/mL, but the PSA velocity exceeds 0.4 ng/mL/year, not only should testosterone be discontinued, but a close examination of the cancer, including a prostate biopsy, may be warranted. The gene discussed is KLK3; the disease is cancer.