48 INTRADUCTAL CARCINOMA IN LOW- AND INTERMEDIATE-RISK PROSTATE CANCER: PATHOLOGICAL AND CLINICAL RELEVANCE

has been described by WHO in 2016 as a unique variant with ductal neoplastic cellular growth. IDC has been reported in 12- 13% on radical prostatectomy specimens. IDC is frequently associated with Grade Group 4 or 5, higher tumor volume and worse prognosis (1). However, IDC foci are frequently missed by biopsy and is not associated to serum PSA elevation (2). The aim of this study is to evaluate IDC incidence and disease recurrence compared to pure adenocarcinoma (PAC) in patients intermediate risk prostate cancer. Patients and Methods: We retrospectively reviewed 361 patients with pre-operative low and intermediate risk prostate cancer who underwent radical prostatectomy between 2016-2020 in a single center. Risk category definition was according to EAU guidelines definition (low-risk: PSA<10 ng/ml and GS<7 and cT1-2a; Intermediate- risk: PSA 10-20 ng/ml or GS 7 or cT2b). Two groups were created based on the presence of IDC versus pure adenocarcinoma (PAC). All specimens have been reviewed by 2 dedicated uro-pathologists. We used Kruskal-Wallis non- parametric test to compare all variables. Groups were compared for index lesion volume, tumor diameter, percentage of cancer, tumor stage, final prostate cancer Grade Group (GG), and number of cancer foci. Backward logistic regression analysis was performed to assess predictive factors for biochemical recurrence (BCR) with a median follow up of 2 years (Table I). Results: Intraductal carcinoma was observed in 39/361 (10.9%) with low and intermediate EAU risk category compared to 32/139 (23%) observed in those with high-risk category. Intraductal carcinoma was identified preoperatively by biopsy only in 3 of 39 patients (7.6%). The IDC group showed, as reported in Table II, significantly larger index tumor diameter (23.4 mm vs. 18 mm, p<0.01) and volume (3.4 ml vs. 1.9 ml, p<0.01), and higher percentage of cancer (9.9% vs. 4.7%, p<0.01) than PAC group. The association of IDC with Gleason pattern 4 was described in most of cases (38/39). Regarding prognostic grade group, we reported in IDC at PAC respectively: GG-1 2.5% (1/39) vs. 18.9% (61/322), GG-2 28.2% (11/39) vs. 58.1% (187/322), GG-3 in 53.8% (21/39) and 18.6% (60/322), GG-4 in 10.2% (4/39) and 1.8% (6/322), respectively. No significant difference was noted for GG-5 (2.4% vs. 5.1%, p=0.6) and number of cancer foci (p=0.2). Regarding pathological stage, the IDC group showed a (p<0.001): pT3a was present in 46.1% and pT3b in 23.1% as compared to 27.9% and 4.1% respectively in the PAC group. After 2-years follow-up, 36 patients presented biochemical recurrence: 5 patients (12.8%) in the IDC group and 31 patients (9.6%) in the PAC group (p=0.7) (Table II). Conclusion: Several studies have demonstrated the clinical significance of IDC, both in needle biopsies and in RP specimens (3, 4). Our study shows that intraductal carcinoma occurs in 10.9% of men with low and intermediate risk of prostate cancer. Nevertheless, needle biopsy has a low sensitivity (7.6%) for IDC. IDC is associated with higher index tumor volume, total percentage ofcancer and a higher proportion of locally advanced disease compared to pure adenocarcinoma. IDC detected in prostate biopsies should be integrated in nomograms to predict pathological stage and lymph node metastases. IDC is also considered an adverse prognostic factor for active surveillance.