SPCG-4
In localized prostate cancer, does radical prostatectomy improve survival and metastatic outcomes compared with watchful waiting?
Absolute Effect
The 15-year analysis estimated an NNT of approximately 17 to avert one prostate-cancer death.
Prostate-cancer death occurred in 63/347 after surgery versus 99/348 with watchful waiting; relative risk 0.56.
Time dependence
The absolute benefit increased with longer follow-up. A later analysis found prostate-cancer mortality ARR rising from 1.7% at 5 years to 17.0% at 30 years, illustrating why a single short-term NNT can be misleading in a disease with a long natural history.
Clinical interpretation
The trial population predates PSA-era contemporary imaging and active surveillance selection, so absolute event rates should not be directly applied to today's low-risk populations.
Treatment burden and limitations
Surgery carries urinary, sexual and perioperative morbidity. Watchful waiting is not equivalent to modern MRI-based active surveillance. The trial included a broad historical spectrum of localized disease.
NNT
NNT ≈17 at 15 years, and approximately 9 using the 11.0-point absolute reduction at 23 years. These are time-specific mortality NNTs and should not be mixed across follow-up horizons.