Tumor Volume on Biopsy of Low Risk Prostate Cancer Managed with Active Surveillance

Purpose: Contemporary clinical guidelines recommend active surveillance of men with low risk prostate cancer. Low risk disease spans any potential volume of Gleason score 6 cancer without sufficient attention to tumor volume in the past. Therefore, we compared tumor characteristics in men at low risk on active surveillance to men treated with radical prostatectomy.

Materials and methods: We evaluated an institutional cohort of 1,633 men with very low risk disease (clinical stage T1c, prostate specific antigen density less than 0.15 ng/ml/cm³, 2 or more positive cores and 50% or greater core involvement) and low risk disease (clinical stage T2a or less, prostate specific antigen less than 10 ng/ml and Gleason score 6 or less). Among patients at low risk we calculated the proportion who failed to meet very low risk volume criteria (greater than 2 positive cores or greater than 50% core involvement). Clinical and pathological metrics in the active surveillance cohort were compared to those in a cohort of men at low risk who underwent radical prostatectomy in the current era of 2011 to 2016.

Results: In the active surveillance cohort 1,119 men (69%) met very low risk criteria and 514 (31%) had low risk disease. In the low risk population only 138 men (27%) harbored higher volume cancer exceeding very low risk criteria compared to 815 (82%) at low risk who underwent radical prostatectomy (p <0.001). Overall the low risk active surveillance population had fewer positive biopsy cores (median 1 vs 3, p <0.001) and a lower maximum percent of core involvement (median 10% vs 40%, p <0.001) compared to patients at low risk who underwent radical prostatectomy.

Conclusions: Data supporting the safety of active surveillance in men at low risk at our institution were derived from a distinct subgroup harboring a limited cancer volume. Until acceptable outcomes are confirmed for higher volume tumors it is important to remain mindful of these limitations before broadly recommending active surveillance to all low risk men.