An updated analysis of studies evaluating the clinical and biochemical outcomes of radiation therapies for clinically localized prostate cancer revealed a lack of high-quality evidence regarding the efficacy of radiation treatment compared with no treatment, according to a review published June 6 in Annals of Internal Medicine. The authors called for additional research to demonstrate or disprove the effectiveness of radiation therapy versus no treatment.

Prostate cancer is the most common cancer among men in the U.S., and widespread prostate-specific antigen (PSA) testing has doubled the incidence of prostate cancer. With earlier diagnosis, the incidence of clinically “silent” T1 tumors increased from 17 percent in 1989 to 48 percent in 2001.

Given the array of treatment options, the reviewers sought to answer two questions:

• What are the benefits and harms of radiation therapy for clinically localized prostate cancer compared with no treatment or no initial treatment (watchful waiting, active surveillance or observation)?
• What are the benefits and harms of different forms of radiation therapy for clinically localized prostate cancer?

The researchers focused on 10 randomized, controlled trials and 65 nonrandomized studies of men with clinically localized prostate cancer (T1-T2, NO-X, MO-X) that reported clinical or biochemical outcomes and were published from January 2007 to March 2011.

After extracting and confirming data from the studies, the researchers rated evidence for comparisons of radiation therapy versus no treatment or no initial treatment and comparisons between treatments as insufficient. The single exception was the strength of evidence for intra-external beam radiation therapy (EBRT) comparisons, which the researchers rated as moderate.

The three randomized controlled trials, two prospective studies and nine retrospective studies that compared EBRT treatments “reported that higher dose EBRT was associated with increased rates of freedom form biochemical failure at five to 10 years compared with lower-dose EBRT,” wrote lead author Raveendhara R. Bannuru, MD, of the Institute of Clinical Research and Health Policy Studies at Tufts Medical Center in Boston, and colleagues.

Other findings suggested that radiation treatments were linked with increased urinary or bowel problems compared with no treatment or no initial treatment and that brachytherapy might be associated with more urinary toxicity than EBRT.

“This updated reviews showed unclear effectiveness of radiation treatments compared with no treatment or no initial treatment of localized prostate cancer on patient survival," the authors concluded. "Similarly, evidence was insufficient to determine whether certain forms of radiation treatment were more effective than others.”

Bannuru and colleagues emphasized the need for further study, specifying that a direct comparative study of appropriately selected patients with localized disease is needed to determine or disprove that suggested benefit of radiation therapy over no initial treatment.