Grade group 2 (10% ≥ GP4) patients have very similar malignant potential with grade group 1 patients, given the risk of intraductal carcinoma of the prostate.

Background: It has been argued that grade group 2 (GG2) with a low Gleason pattern 4 (GP4) proportion should be an indication for active surveillance (AS) of prostate cancer (PCa). However, the cut-off GP4 proportion for AS remains unclear. Here, we evaluated the effect of GP4 proportion and IDC-P on cancer recurrence following radical prostatectomy (RP) in GG1 and GG2 patients, and identified candidates for AS.

Methods: We retrospectively evaluated 646 patients with PCa who underwent RP between 2005 and 2014, and whose specimens were of GG1 or GG2 status.

Results: The GGs were as follows: GG1, 25.2% (n = 163); GG2 (5% ≥ GP4), 11.4% (n = 74); GG2 (5% < GP4 ≤ 10%), 25.9% (n = 167); and GG2 (20% ≤ GP4), 37.5% (n = 242). IDC-P was detected in 26 patients (4%), i.e., in 2/167 GG2 (5% < GP4 ≤ 10%; 1%) cases and 24/242 GG2 (20% ≤ GP4; 10%) cases. GG2 patients with IDC-P exhibited a significantly poorer prognosis than did those without IDC-P (P < 0.0001), as did GG2 (20% ≤ GP4) patients without IDC-P (P < 0.05). The GG2 (5% ≥ GP4) and (5% < GP4 ≤ 10%) groups exhibited prognoses similar to those of the GG1 patients. In multivariate analysis, GG2 (20% ≤ GP4) without IDC-P, the presence of IDC-P, and the prostate-specific antigen level at diagnosis significantly predicted prognosis (P < 0.05, < 0.0001, and < 0.0001, respectively).

Conclusion: Our findings suggest that GG2 (GP4 ≤ 10%) patients could be indicated for AS, similar to GG1 patients, given the risk of IDC-P tumors.