Investigators found that prostate-specific antigen (PSA) testing may be a poor surrogate for patient outcome in the contemporary era and may not be as useful for men with localized prostate cancer as many researchers thought, according to a study published in the American Journal of Clinical Oncology.1

The researchers analyzed data from 12 randomized controlled trials of external beam radiation treatment for 6884 patients with non-metastatic prostate cancer, with a median age of 69 years.

In addition to looking at outcomes with PSA testing, they examined long-term outcomes and deaths from any cause. Researchers found little correlation between PSA outcomes and patient survival.

Lead study investigator Nicholas Zaorsky, MD, who is a resident physician in radiation oncology at Fox Chase Cancer Center in Philadelphia, PA, said many clinical trials for patients with prostate cancer are using PSA as a proxy for how long patients will survive. However, this study showed that reliance on the PSA test was not as useful as clinicians have been led to believe. He said the findings have broad implications for the design of future clinical trials and the interpretation of current and previous studies.

“In the past 30 years, clinical trials of radiation therapy for prostate cancer have been trying to safely increase the dose delivered to the prostate. Among these trials, we have seen improvements in PSA outcomes with higher dose, and this is supposedly a good proxy for development of metastasis and how long patients will survive. However, in our analysis, we did not see correlation between the dose and development of metastasis or improvement in survival,” said Dr Zaorsky.

The researchers analyzed how increasing the prostate cancer biologically equivalent dose (BED) of external radiation therapy (RT) was correlated with freedom from biochemical failure (FFBF). They also looked at FFBF, overall survival (OS), distant metastasis (DM), and cancer-specific mortality (CSM). The investigators examined genitourinary and gastrointestinal (GI) toxicities.

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They found increasing BED correlated with improved FFBF and the 10-year absolute improvement was 9.6% for low-risk patients and 7.2% for intermediate-risk patients. However, there was no correlation with improvement of OS, DM, or CSM. The researchers reported that BED escalation was not correlated with increased acute toxicities but it was correlated with increased late GI toxicities in patients treated with 3-dimensional conformal RT (3D-CRT).