A test used to detect prostate cancer can also help doctors know when treatment is working. A man’s prostate specific antigen, or PSA, level after seven months of hormone therapy for advanced prostate cancer predicted how long he would survive, according to a new multicenter study conducted by the Southwest Oncology Group and led by researchers at the University of Michigan Comprehensive Cancer Center.

The study evaluated 1,345 men with prostate cancer that had spread to distant parts of the body. The men were treated with seven months of androgen deprivation therapy, a treatment designed to block the effects of hormones on the cancer. PSA levels were monitored throughout the treatment. The researchers found that men whose PSA dropped below 4.0 ng/ml had a quarter the risk of dying compared to those whose PSA was more than 4.0.

Results of the study appear in the Aug. 20 issue of the Journal of Clinical Oncology.

“Our analysis showed that a low or undetectable PSA after seven months of androgen deprivation therapy is a powerful predictor of risk of death in patients with new metastatic prostate cancer. This could allow oncologists to identify patients who are unlikely to do well with this treatment long before they develop clinical signs of treatment resistance,” says lead study author Maha Hussain, M.D., professor of internal medicine at the U-M Medical School.

The researchers found 69 percent of the men maintained a PSA level of less than 4.0 ng/ml after seven months of treatment and 43 percent had an undetectable level of PSA at that time. Patients whose PSA was higher than 4.0 at the end of seven months survived 13 months, while patients whose PSA dropped below 4.0 but above 0.2 lived 44 months and those whose PSA was undetectable, below 0.2 ng/ml, lived 75 months.

The men in the study were enrolled in a Phase III SWOG trial in which they would receive additional treatment after the seven months of initial hormone therapy. That study seeks to accrue 1,512 men. The patient’s PSA level before beginning treatment must be at least 5.0 ng/ml to qualify for the study.

A PSA test measures the level in the blood of prostate specific antigen, an enzyme produced by the prostate gland. It is generally used as an initial screening test to detect prostate cancer.

“What is attractive about using PSA to predict survival in metastatic prostate cancer is that it is an easily measurable factor. These findings could help patients avoid ineffective treatment and could help researchers design further trials,” Hussain says.

University of Michigan Health System