Intraductal carcinoma of the prostate (IDCP) is known as a poor prognostic factor in patients with prostate cancer, highlighting the importance of its diagnosis to better predict prostate cancer outcomes. Various reports exist on IDCP prevalence, with rates in prostatectomy specimens ranging from 43.7% to 0.003%. Some studies suggest a higher prevalence among Asians, though few compare IDCP rates internationally. We reevaluated the IDCP positivity rate in prostatectomy specimens from Showa University Hospital (SUH, Japan) and Queen's Medical Center (QMC, Hawaii) for cross-regional comparison.

We examined 178 from Showa University Hospital and 118 prostatectomy cases from Queen's Medical Center between April 2020 and April 2024. Patient background data, including PSA levels, age, race, and postoperative pathology, were extracted. Uropathologists reevaluated IDCP prevalence based on Guo and Epstein’s criteria. Statistical analysis was performed using SPSS, with significance set at P < 0.05.

After excluding cases where hormone therapy was administered or slides were unavailable (13 from SUH, 4 from QMC), the study included 165 cases from SUH and 114 from QMC. The average age was 68.7 years at SUH and 68.3 years at QMC. SUH had 100% Asian patients, while QMC had 29.8% Caucasians, 2.6% African Americans, 55.2% Asians, 9.6% Native Hawaiians, 0.8% Native Americans, and 1.7% unknown. PSA levels at biopsy were 12.6 ng/mL at SUH and 10.2 ng/mL at QMC (P = 0.11). IDCP positivity was 23.0% at SUH and 28.1% at QMC, with no significant difference between the two populations (P = 0.34). Additionally, when IDCP prevalence was evaluated by ethnicity at QMC, no significant differences were observed among Asians, Whites and Native Hawaiians. After propensity score matching, differences in patient backgrounds were minimized, and the matched analysis also showed no significant difference in IDCP prevalence (p=0.09). Multivariate analysis identified extraprostatic extension (EPE) as the only significant risk factor for IDCP (p<0.05).

Our study demonstrated no significant differences in IDCP prevalence across racial or institutional lines when using a standardized diagnostic criteria. This finding suggests that IDCP development is not limited to specific racial genetic predispositions. The results underscore the importance of international standardization of IDCP diagnosis and epidemiological evaluation. Further research is needed to explore potential genetic and environmental factors contributing to IDCP development.