As reported in The New England Journal of Medicine by van As et al, the phase III PACE-B trial has shown noninferiority of stereotactic body radiotherapy (SBRT) vs conventionally fractionated radiotherapy in biochemical or clinical failure in patients with low- to intermediate-risk localized prostate cancer.

Study Details

In the open-label noninferiority trial, 874 patients from sites in the United Kingdom, Ireland, and Canada were randomly assigned between August 2012 and January 2018 to receive SBRT (n = 433) or conventional (control) radiotherapy (n = 441). Patients had stage T1 or T2 disease, Gleason score of 3+4 or less, and prostate-specific antigen level ≤ 20 ng/mL. SBRT consisted of 36.25 Gy in 5 fractions over 1 or 2 weeks; control radiotherapy consisted of 78 Gy in 39 fractions over 7.5 weeks or 62 Gy in 20 fractions over 4 weeks. Androgen-deprivation therapy was not permitted. The primary outcome measure was freedom from biochemical or clinical failure, with a noninferiority margin for SBRT of 6% (hazard ratio [HR] = 1.45).

Freedom From Biochemical or Clinical Failure

Median follow-up was 74.0 months. At 5 years, the proportion of patients with freedom from biochemical or clinical failure was 95.8% (95% confidence interval [CI] = 93.3%–97.4%) in the SBRT group vs 94.6% (95% CI = 91.9%–96.4%) in the control radiotherapy group (hazard ratio [HR] = 0.73, 90% CI = 0.48–1.12, P = .004 for noninferiority). A post hoc test for superiority was not significant (HR = 0.73, 95% CI = 0.44–1.21, P = 0.22). Hormone therapy was started in 10 patients in the SBRT group and 19 in the control radiotherapy group (HR =  0.55, 95% CI = 0.26–1.20).

Toxicity

At 5 years, the cumulative incidence of late Radiation Therapy Oncology Group grade ≥ 2 genitourinary toxic effects was 26.9% (95% CI = 22.8%–31.5%) in the SBRT group vs 18.3% (95% CI = 14.8%–22.5%) in the control radiotherapy group (P < .001). The cumulative incidence of late grade ≥ 2 gastrointestinal toxic effects was 10.7% (95% CI = 8.1%–14.2%) in the SBRT group vs 10.2% (95% CI = 7.7%–13.5%) in the control radiotherapy group (P = .94).

The investigators concluded: “Five-fraction SBRT was noninferior to control radiotherapy with respect to biochemical or clinical failure and may be an efficacious treatment option for patients with low-to-intermediate-risk localized prostate cancer as defined in this trial.”

Nicholas van As, MD, of Royal Marsden Hospital, London, is the corresponding author of The New England Journal of Medicine article.

Disclosure: The study was funded by Accuray and others. For full disclosures of the study authors, visit nejm.org.