Undetectable PSA Possible With Radiation

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CHICAGO – Improved radiotherapy techniques have made it possible for men to achieve reductions in PSA to below detectable levels following radiation treatment for prostate cancer, according to new findings presented here at the American Society for Radiation Oncology's 51st Annual Meeting. These undetectable levels are associated with a significantly reduced risk of biochemical recurrence.

Researchers at Fox Chase Cancer Center in Philadelphia reported that undetectable PSA (UDPSA) can commonly be achieved following radiation therapy alone. Additionally, they said men who achieve UDPSA have an extremely good prognosis, independent of age.

“With high quality radiation, whether it is from an implant or external beam, it is possible to get really low PSAs,” said study investigator Eric Horwitz, MD, Chairman of the Department of Radiation Oncology at Fox Chase. “And if you do, you have a really good chance of being cured. We used to tell our patients that they wouldn't have an undetectable or really low PSA, but we are seeing that some do now after radiation.”

After surgery, patients are expected to have an undetectable PSA level because the entire prostate has been removed.  However, patients treated with radiotherapy alone may still have viable prostate tissue after treatment because the radiation beam is narrowly focused on the tumor. Therefore, radiation oncologists have not expected their patients to have the same very low PSA scores as surgical patients. That expectation is now changing, according to Dr. Horwitz.

He and his colleagues examined patient records for 1,330 men with prostate cancer who were treated with radiation therapy alone at Fox Chase between 1989 and 2005. The study population had a median follow-up of 74 months.

A total of 154 men (12%) achieved UDPSA at a median time of 32 months after the end of treatment. These patients had a significant 59% decreased risk of biochemical failure compared with men who had detectable PSA levels, after adjusting for age, pretreatment PSA level, Gleason score, and radiotherapy modality, and radiation dose.

The seven-year rates of biochemical failure were 6.7% for the UDPSA group and 18.9% for the detectable group. The seven-year rates of distant metastases were 0.9% and 3.1%, respectively.

The study included patients who had Gleason scores of 7 or less, PSA levels of 10 ng/mL or less, and stage T2c tumors or less. The study excluded patients who were receiving androgen deprivation therapy, had prior prostate surgery, or were participating in a clinical trial. The investigators defined UDPSA as a PSA level below the laboratory minimum value at the time of testing or a PSA level of 0.1 ng/mL. 

“What we found is that patients can do fantastic,” Dr. Horwitz told Renal & Urology News.  “I think we have found that with quality radiation, whether it is an implant or IMRT [intensity-modulated radiation treatment], you actually can achieve extremely low PSAs, and if you do, you have a durable and successful treatment.”

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