Active surveillance for intermediate risk prostate cancer: the Manitoba Prostate Center experience

OBJECTIVES: To report long-term oncological outcomes of men with intermediate-risk prostate cancer managed with active surveillance at a single centre. SUBJECTS/PATIENTS AND METHODS: We retrospectively analysed a prospectively maintained Manitoba Prostate Centre active surveillance database. Included were men with disease classed per National Comprehensive Cancer Network risk categories: very low-, low-, favourable intermediate-, and unfavourable intermediate-risk prostate cancer managed with surveillance (2004-2023). Active surveillance involved serial prostate-specific antigen testing, digital rectal exam, and confirmatory/surveillance biopsies. Outcomes were treatment-free survival, metastasis-free survival, prostate cancer-specific survival, overall survival, and biopsy grade progression. Kaplan-Meier estimated survival; Cox regression evaluated variables associated with outcomes. RESULTS: Among 561 men, the median age was 65 years (interquartile range 59-69) and the median follow-up was 4.4 years. Overall, 256 men (45.6%) transitioned to definitive treatment. Five-year treatment-free survival declined stepwise by risk group: 84.8% in very low-risk, 61.4% in low-risk, 50.0% in favourable intermediate-risk, and 21.4% in unfavourable intermediate-risk disease (P < 0.001). On multivariable analysis, older age, higher prostate-specific antigen density, and grade group ≥2 were independently associated with earlier treatment. Metastatic progression and prostate cancer-specific mortality were rare across the cohort, with higher event rates observed among patients with unfavourable intermediate-risk disease. CONCLUSIONS: In this real-world active surveillance cohort, the likelihood of remaining on surveillance differed substantially by baseline risk, with unfavourable intermediate-risk disease associated with earlier transition to treatment and higher risks of disease progression. Older age, higher prostate-specific antigen density, and grade group ≥2 were independently associated with discontinuation of active surveillance. Despite less intensive surveillance protocols, rates of metastatic progression and prostate cancer-specific mortality remained low, particularly among patients with low-risk and favourable intermediate-risk disease, supporting active surveillance as a viable management strategy in carefully selected men beyond low-risk disease.