CHICAGO—Androgen-deprivation therapy (ADT) “can be safely reduced from 36 to 18 months without compromising outcomes,” in patients with localized high-risk prostate cancer, results of a study presented at the 2013 American Society of Clinical Oncology (ASCO) Annual Meeting has found.

In fact, ADT delivered for 18 months may represent a threshold effect, said Abdenour Nabid, MD, of the Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Quebec City, Canada.

Between October 2000 and January 2008, Dr. Nabid and colleagues compared outcomes between 36 and 18 months of ADT in patients with high-risk prostate cancer treated with radiotherapy (RT) in the PCS IV trial.

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Patients with node-negative high-risk prostate cancer, defined as T3-4, PSA greater than 20 ng/mL or Gleason score higher than 7, were randomly assigned to pelvic RT (whole pelvis 44 Gy for 4.5 weeks and prostate 70 Gy for 7 weeks) and neoadjuvant, concomitant, or adjuvant ADT comprising bicalutamide 50 mg for 1 month and goserelin 10.8 mg every 3 months for 36 months (n=310) or 18 months (n=320).

Overall survival (OS), disease specific survival (DSS), and quality of life were the primary endpoints.

Patient characteristics were well balanced between the two arms. Median age was 71 years; median PSA, 16 ng/mL; and median Gleason score, 8. Most patients had T2-T3 disease.

At a median follow-up of 78 months (6.5 years), 80 patients (25.8%) in the RT plus ADT for 36 months arm and 85 (26.6%) in the RT plus ADT for 18 months arm had died (P=0.829), 113 from causes other than prostate cancer.

For the 18-month versus 36-month arms, the hazard ratio for OS was 1.15 (95% CI: 0.85-1.56; P=0.366) and for cancer-specific survival, 1.07 (95% CI: 0.62-1.84; P=0.819). Five-year OS rates were 91.1% (95% CI: 87.9-94.3) versus 86.1% (95% CI: 82.3-90.0; P=0.06), and 5-year DSS rates, 96.6% (95% CI: 94.5-98.7) versus 95.3% (95% CI: 92.8-97.7; P=0.427).

Ten-year OS rates were 61.9% (95% CI: 54.1-69.7) versus 58.6% (95% CI: 49.8-67.4; P=0.275), and 10-year DSS rates, 84.1% (95% CI: 77.6-90.6) versus 83.7% (95% CI: 76.3-91.1; P=0.819), respectively.

No significant differences in the rates of biochemical, regional, or distant failure between arms were observed.

With the 18-month versus the 36-month schedule, “duration of side effects and treatment costs can be significantly reduced,” Dr. Nabid said. Treatment impact on quality of life is now under analysis. More than 9,638 questionnaires have been answered over the past 12-plus years.

This study was funded by a grant from AstraZeneca Pharmaceuticals.