Huggins established a method to measure the effect hormone changes have on prostatic function. He found out that castration or estrogen administration led to glandular atrophy, which could be reversed by re-administration of androgen. In 1941 the beneficial effect of androgen ablation on metastatic prostate cancer was realised when Huggins and Clarence Hodges treated patients by either castration or estrogen therapy. They monitored the prostate size and therapeutic efficacy by measuring serum prostatic acid phosphatase levels and concluded that androgenic activity in the body influences prostate cancer, at least with respect to serum phosphatase. Huggins was the first to use a systemic approach to treat prostate cancer.