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

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Abstract
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.

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