Swift drop in PSA after radiation therapy called portent of better survival

San Antonio (Oct. 12, 2004) – New research presented in Atlanta last week suggests the embattled PSA test may yet be a useful tool in the early detection of prostate cancer. Researchers from the San Antonio Cancer Institute (SACI) – a National Cancer Institute-designated Cancer Center that is a partnership of The University of Texas Health Science Center at San Antonio and the Cancer Therapy & Research Center – report that men who had a rapid drop in PSA after receiving radiation therapy were roughly five times less likely to die of the disease within 10 years than men whose PSA levels did not drop so quickly.

“Our claim is that as early as three months after radiation therapy, we can use PSA to separate men into two groups – men who are likely to die of their disease and men who are not so likely,” said Sean X. Cavanaugh, M.D., a SACI member and Ph.D. candidate from the Health Science Center’s department of radiation oncology. He presented the findings Oct. 4 in Atlanta at the 46th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO). In addition to SACI, co-authors of the study are from the Cleveland Clinic and the M.D. Anderson Cancer Center Orlando.

Dr. Cavanaugh and five co-authors examined data from 918 men who received external-beam radiation therapy at the Cleveland Clinic and whose outcomes were already known. The researchers charted disease-specific survival (deaths related to prostate cancer only) and overall survival (deaths from all causes). Men whose PSA levels were lower than 3.0 ng/ml (nanograms per milliliter) three months after therapy had a 96.1 percent disease-specific survival rate, compared to an 81.7 rate for men who had readings above 3.0. The overall survival rate also was higher.

“Those patients who reach lower thresholds faster on the PSA scale have better disease-specific survival and overall survival,” Dr. Cavanaugh summarized. “Our argument is, look, the early PSA matters, and all patients should not be managed the same way.”

Traditionally, two tests have been used to detect prostate cancer – digital rectal examination and prostate-specific antigen (PSA). The PSA test measures a protein that is made generally only by the prostate and that is increased in men with prostate cancer. If either the DRE or PSA is suspicious for prostate cancer, the physician may recommend a prostate biopsy. If prostate cancer is present, treatment options include radiation therapy, hormone therapy and surgical removal of the prostate.

The PSA test has taken its share of hits. This past May, a study revealed that 15 percent of men with supposedly “normal” PSA readings later developed cancer, including some men whose cancers were considered high grade. The lead author of that national study was Ian M. Thompson Jr., professor and deputy chair of surgery at the Health Science Center and director of the SACI Cancer Prevention and Population Science Program. He has said that while PSA still has value, a more-effective way of ascertaining a man’s risk of prostate cancer is needed.

The ASTRO poster presentation is titled “Time and PSA Threshold Modeling Predicts Overall and Disease-Free Survival as Early as Three Months after External Beam Radiation Therapy for Prostate Cancer.” Authors are Dr. Cavanaugh, a medical resident at the Health Science Center who is working on a Ph.D. in human imaging; Patrick Kupelian, M.D., of the Cleveland Clinic and the M.D. Anderson Cancer Center Orlando; Patrick Bradshaw and Dave Fuller of the Health Science Center; Chandra Reddy from the Cleveland Clinic; and Martin Fuss, M.D., Ph.D., of the Health Science Center and the Cancer Therapy & Research Center.

Dr. Fuss is the chairman of Dr. Cavanaugh’s Ph.D. dissertation committee and his mentor in clinical training in radiation oncology. “For the last several years, he has taken a daily personal interest in training me as a scientist and as an oncologist,” Dr. Cavanaugh said.

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