In the largest study of its kind to date, Mayo Clinic researchers report that prostate specific antigen (PSA) kinetics, both velocity and doubling time, can be used to predict disease progression and likelihood of death after radical prostatectomy surgery, suggesting that this could be used to guide treatment decisions.
Study results are published in the December issue of The Journal of Urology.
"The level of PSA in the blood has less prognostic value than we previously thought, and we don't have another serum marker to help us," says Michael Blute, M.D., Mayo Clinic urologist and lead investigator of the study. "It was important for us to find other ways to look at PSA data and translate that into information that will save lives, and I believe we have done that."
Prostate cancer is the second most common cancer in men (skin cancer is first) and the second leading cause of cancer death in American men, exceeded only by lung cancer. This year, the American Cancer Society estimates 232,000 new cases of prostate cancer will be diagnosed. While one in six men will be diagnosed with prostate cancer in his lifetime, only one in 33 will die of it. However, because it causes disability and death, finding new strategies to better target treatments is an important public health goal.
Dr. Blute and his fellow researchers reviewed the records of 2,290 patients with multiple preoperative PSA measurements, as well as 5,176 patients with only one preoperative measurement, looking at the rate at which PSA increased in the body -- thought to indicate cancer growth. This was measured as both the PSA velocity (PSAV), the rate of increase in PSA levels over time, and the PSA doubling time (PSADT), a measure of how quickly PSA levels double. The researchers found that while PSAV is simpler to calculate, PSADT may be a better indicator of untreated prostate cancer.
Over an average follow-up period of about seven years, cancer spread or recurrence, and deaths from cancer were recorded. Biochemical progression was noted in 25.5 percent of the patients, clinical progression in 6.8 percent and cancer death in 1.8 percent. PSAV and PSADT both predicted progression and death. PSAV greater than 3.4 ng/ml yearly correlated to men being 6.54 times more likely to die than those with lower PSAV. PSADT quicker than 18 months correlated to the risk of death being 6.22 times higher than for those with longer PSADT.
"This provides valuable pretreatment prognostic factors for prostate cancer," says primary author Shomik Sengupta, M.D. "We hope that our work will help in the doctor-patient discussion and result in more informed decisions relating to observation, intervention and adjuvant treatment."
The study group consisted of patients who had undergone radical prostatectomy for prostate cancer between 1990 and 1999 at Mayo Clinic. Preoperative and postoperative PSA measurements were obtained from referring physicians and/or Mayo laboratory testing.
Other Mayo Clinic researchers who contributed to this study include Robert Myers, M.D.; Jeffrey Slezak; Eric Bergstralh; and Horst Zincke, M.D., Ph.D.