SAN ANTONIO, TX—Overall survival was statistically improved by adding a 24-month course of antiandrogen therapy (AAT) during and after salvage radiotherapy (RT), compared with salvage RT alone. These findings, in men with rising serum prostate-specific antigen (PSA) levels and whose prostate cancer was treated with radical prostatectomy (RP), come from long-term results of a clinical trial conducted by the Radiation Therapy Oncology Group (RTOG), now conducting research as NRG Oncology.

The RTOG 9601 study results were presented at the plenary session of the 2015 American Society for Radiation Oncology (ASTRO) Annual Meeting. The study also revealed that adding AAT to salvage RT reduces prostate cancer metastasis and death without increasing radiation toxicity.

“Over the last 25 years, many men with intermediate-risk prostate cancer have undergone RP, yet many will face recurrence subsequently with a rising PSA,” said lead study author William U. Shipley, MD, FACR, FASTRO, who is the Andres Soriano Distinguished Professor of Radiation Oncology at Massachusetts General Hospital and Harvard Medical School, both in Boston, Massachusetts.

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“Our results show that salvage RT plus peripheral androgen blockade (AAT with bicalutamide), when compared with RT plus a placebo, improved long-term overall survival and reduced death from prostate cancer without adding significantly to radiation toxicity. Because prostate cancer progresses slowly, follow-up of over 12 years was necessary to demonstrate a statistically better patient survival with combined AAT and RT.”

With median follow-up now 12.6 years, the study results showed actuarial overall survival at 10 years was 82% for the RT plus AAT arm and 78% for the RT plus placebo arm (P=.036). The 12-year incidence of prostate cancer-related deaths was 2.3% for the RT plus AAT arm, compared with 7.5% for the RT plus placebo arm.

At 12 years, the cancer had metastasized in 51 patients (14%) in the RT plus AAT arm, compared with metastasis in 83 patients (23%) in the RT plus placebo arm. In addition, late bladder and bowel toxicity were low and similar in both groups, whereas 70% of men in the RT plus AAT arm reported swelling of the breasts, compared with 11% in the RT plus placebo arm.

Conducted at sites across the United States and Canada from 1998 to 2003, the RTOG 9601 trial enrolled 761 men with prostate cancer who had undergone RP and subsequently developed elevated PSA levels. The patients were randomized to receive either salvage RT plus placebo (377 patients) or salvage RT plus AAT (384 patients).

“Further statistical analyses, which are underway, may identify subgroups of patients who may not benefit from hormone therapy added to salvage RT and other subgroups for whom it may be especially beneficial,” said Shipley. “Also, because antiandrogen therapy, which suppresses testosterone production, is now used more commonly than peripheral androgen blockade with AAT, its use should be evaluated.”