Importance of Testing PSA Soon After Radiotherapy

Thu 02-Oct-2003 The success or failure of radiation therapy for prostate cancer may be predicted as early as three months after completion of therapy, rather than waiting one to two years as conventional wisdom indicates, a new study suggests.

The success or failure of radiation therapy for prostate cancer may be predicted as early as three months after completion of therapy, rather than waiting one to two years as conventional wisdom indicates, a new study from The University of Texas Health Science Center at San Antonio (UTHSC) suggests.

Men whose blood PSA values stayed above important threshold levels three months after radiotherapy were 30 percent more likely to suffer a recurrence of cancer than men whose PSA values sank lower. The authors studied the prognostic value of early PSA changes in order to establish a model for analyzing improvements in radiation therapy, including intensity-modulated radiation therapy, a rapidly developing technique that pinpoints tiny radiation beams to destroy tumors but spare surrounding healthy tissues.

"Patients generally have their PSA tested soon after therapy, but unless there is a dramatic increase, many physicians wait a year or two and analyze the trend before interpreting the information. My colleagues and I disagree with that approach," said Sean X. Cavanaugh, M.D., lead author of the study and fourth-year resident in the UTHSC department of radiation oncology. "We found that PSA levels at three or six months after radiotherapy were significantly prognostic for long-term outcome. Analysis of early PSA response enables us to accurately identify those patients who have an 80 percent or better chance of being cured of prostate cancer. Once confirmed by follow-up studies, this method may help us to identify men who will most benefit from the addition of hormone therapy, which has some serious side effects and should not be started in all men."

Dr. Cavanaugh and his co-authors studied blood samples of 855 men treated at the Cleveland Clinic with external beam radiotherapy. They compared the early PSA response to the clinical outcome of the patients. The average patient in the study was followed for more than six years. None of the men underwent hormone therapy, which may lower PSA levels. The study also did not examine men whose cancers had spread outside the prostate and who have a much worse prognosis for survival.

Many physicians focus on the time it takes PSA to stabilize or reach a minimum after radiotherapy (known as PSA nadir). A lack of PSA increase during the first few years is associated with a more favorable outcome. Dr. Cavanaugh advocates evaluating every patient at three months after radiotherapy. "At the three-month mark in this study, we established that if a patient's PSA level was lower than 3.0 ng/ml (nanograms per milliliter), his chance of long-term, relapse-free survival was 87.8 percent, compared to the patients whose levels were above 3.0 at three months and who had only a 57.2 percent chance of relapse-free survival."

Dr. Cavanaugh, who is simultaneously completing a residency in radiation oncology and a Ph.D. in human imaging in the UTHSC Graduate School of Biomedical Sciences, will present the findings Oct. 20 in Salt Lake City at the 45th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO). "A number of scientific papers have been written on PSA, and we used some of the excellent work by other authors as a starting point for our research," Dr. Cavanaugh said. "Our approach was thorough and novel, and I think we have produced some of the most important work to date on the prognostic value of early PSA changes after radiotherapy."

"This seminal work of Dr. Cavanaugh's will alter the way that PSA is used as a prognostic factor after radiation therapy," said Charles R. Thomas Jr., associate professor and vice chairman of the UTHSC department of radiation oncology. Co-authors are Patrick Kupelian, M.D., a radiation oncologist and prostate cancer researcher at the Cleveland Clinic and the M.D. Anderson Cancer Center Orlando in Orlando, Fla; Patrick Bradshaw, biostatistician at UTHSC's Center for Epidemiology and Biostatistics; and Chandra Reddy from the Cleveland Clinic. Martin Fuss, M.D., a radiation oncologist at UTHSC, is both the senior author of the study and Dr. Cavanaugh's research mentor.

In a related study to be presented at the ASTRO meeting, Drs. Fuss and Cavanaugh worked with UTHSC graduate students Lindsey Voeltz and Dave Fuller; Bill Salter, Ph.D., assistant professor of radiation oncology; and Terence Herman, M.D., chairman and professor of radiation oncology, evaluating early changes in PSA following intensity-modulated radiation therapy (IMRT) with and without daily stereotactic ultrasound targeting of the prostate. With respect to early PSA decline, patients treated with IMRT aided by ultrasound-based, image-guided targeting fared better than those who had IMRT only.

More than 200,000 men worldwide die from prostate cancer every year, including about 30,000 in the United States. The PSA test emerged more than a decade ago as a promising way to detect and follow the course of the disease. Prostate-specific antigen is a protein produced only by the cells of the prostate gland. PSA levels can rise because of cancer or non-cancerous conditions, and PSA tests also may result in false positives, according to the National Cancer Institute.

This story last Updated 2003-10-06 by J. Strax.

Source: The University of Texas Health Science Center at San Antonio