Detection of intraductal carcinoma in prostate cancer patients with small tumor volume

The purpose of this study was to investigate intraductal carcinoma of the prostate (intraductal carcinoma) and significant cancer (SC) in patients with small tumor volume (<0.5 cm³ ) in prostatectomy specimens.

Data from 639 patients undergoing radical prostatectomy between April 2006 and December 2017 at Chiba University Hospital and 2 affiliated institutions were retrospectively reviewed. Tumor volume in prostatectomy specimens was measured, and with a tumor volume of less than 0.5 cm³ , the presence of intraductal carcinoma and SC was examined. SC was defined as one that did not meet the definition of pathological insignificant cancer (organ-confined cancer, Grade Group 1, tumor volume < 0.5 cm³ ). The number of patients who met four active surveillance (AS) protocols was also examined.

A total of 83 patients with tumor volume < 0.5 cm³ were identified in this study population (SC: 43 patients [52%], intraductal carcinoma: 5 patients [6%]). The median follow-up was 34.6 months (range: 18-57 months). Four (5%) developed biochemical recurrence. The number of positive biopsy cores ≥ 2 was an independent predictor of SC in patients with tumor volume < 0.5 cm³ (hazard ratio: 4.39; 95% confidence interval: 1.67-11.56; p = 0.003). In tumor volume < 0.5 cm³ , tumor volume was significantly correlated with the International Society of Urological Pathology Grade Group (1 vs. 4-5, p = 0.002) and the presence of intraductal carcinoma (p = 0.004). In intraductal carcinoma-positive cases, four of five patients (80%) had the predictor of SC, which was two or more positive biopsy cores. Of the four AS protocols, the criteria for Prostate Cancer Research International: Active Surveillance were met most frequently in 46 cases (55%) of tumor volume less than 0.5 cm³ if targeted biopsy by magnetic resonance imaging was available.

The results of the present study suggest that intraductal carcinoma was present even in cases with small tumor volumes. Grade Group and intraductal carcinoma showed a positive correlation with tumor volume.