3+4 = 6? Implications of the stratification of localised Gleason 7 prostate cancer by number and percentage of positive biopsy cores in selecting patients for active surveillance.

OBJECTIVE: To determine whether the number and percentage of positive biopsy cores identify a Gleason 3+4 prostate cancer (PC) subgroup of similar biologic behaviour to Gleason 3+3.

MATERIAL AND METHOD: An observational post-radical prostatectomy study was conducted of a cohort of 799 patients with localised low-risk (n=582, Gleason 6, PSA <10ng/ml and cT1c-2a) and favourable intermediate PC (n=217, Gleason 3+4, PSA ≤10 ng/ml and pT2abc). The Gleason 3+4 tumours were stratified by number (≤3 vs.>3) and by percentage of positive cores (≤33% vs. >33%). We analysed the tumours' association with the biochemical recurrence risk (BRR) and cancer-specific mortality (CSM). We conducted various predictive models using Cox regression and estimated (C-index) and compared their predictive capacity.

RESULTS: With a median follow-up of 71 months, the BRR and CSM of the patient group with Gleason 3+4 tumours and a low number (≤3) and percentage (≤33%) of positive cores were not significantly different from those of the patients with Gleason 6 tumours. At 5 and 10 years, there were no significant differences in the number of biochemical recurrences, the probability of remaining free of biochemical recurrences, the number of deaths by PC or the probability of death by PC between the 2 groups. In contrast, the patients with Gleason 3+4 tumours and more than 33% of positive cores presented more deaths by PC than the patients with Gleason 6 tumours. At 10 years, the probability of CSM was significantly greater. This subgroup of tumours showed a significantly greater BRR (RR, 1.6; P=.02) and CSM (RR, 5.8, P≤.01) compared with the Gleason 6 tumours. The model with Gleason 3+4 stratified by the percentage of positive cores significantly improved the predictive capacity of BRR and CSM.

CONCLUSIONS: Fewer than 3 cores and a percentage <33% of positive cores identifies a subgroup of Gleason 3+4 tumours with biological behaviour similar to Gleason 6 tumours. At 10 years, there were no differences in BRR and CSM between the 2 groups. These results provide evidence supporting active surveillance as an alternative for Gleason 3+4 tumours and low tumour extension in biopsy.