Grading of prostate cancer: the impact of including intraductal carcinoma on the overall Grade Group assigned in diagnostic biopsies.

Abstract

The Gleason score/Grade Group (GrG) is a key parameter for clinical decision-making in prostate cancer. The World Health Organization currently recommends that intraductal carcinoma of the prostate (IDCP) should not be factored into the GrG; however, grading of IDCP is controversial, with variability among genitourinary pathologists. The aim of this study was to evaluate the impact of grading of the IDCP component on the final GrG in prostate biopsies. The study included 123 prostate biopsies (12 cores +/- additional MRI-targeted cores) with GrG1-GrG4 invasive carcinoma and IDCP. All cases were graded by a genitourinary pathologist using two different methods: (i) grading of invasive carcinoma only; and (ii) grading of both invasive carcinoma and IDCP. The overall GrG, excluding the IDCP component, was GrG1 in 3% (n=4) of cases, GrG2 in 37% (n=45), GrG3 in 52% (n=64), and GrG4 in 8% (n=10). When the IDCP component was included in grading, the overall GrG changed in 28 cases (23%). The GrG increased by one grade in 15 of 28 cases (54%), and by two or more grades in 13 of 28 cases (46%). Upgrading was due to comedonecrosis (39%, 11/28), solid growth (4%, 1/28), or an increased proportion of Gleason grade 4 (57%, 16/28). Although the GrG was unchanged in the majority of cases, grading of IDCP altered the final GrG in a significant minority of biopsies in this series, and often by more than one grade, which may have important implications for risk categorisation of individual patients. These findings highlight the need for consensus on grading of IDCP in routine practice, and the optimal method of incorporating IDCP into clinical risk models for patient management.