Genetic Analysis of Intraductal Carcinoma of the Prostate Detected in High-Grade Prostatic Intraepithelial Neoplasia Cases

Background The accurate diagnosis of intraductal carcinoma of the prostate (IDC-P) is occasionally challenging due to the similarity in pathological morphology between IDC-P and high-grade prostatic intraepithelial neoplasia (HGPIN). In this report, we reviewed the pathology of cases previously diagnosed as HGPIN to search for IDC-P cases effectively. In addition, we examined whether those cases had genetic abnormalities. Methods We reviewed 98 patients with HGPIN who underwent prostatectomy at our hospital between 2011 and 2021. They were reviewed by three pathologists to search for IDC-P findings by adding immunostaining for basement membrane markers. Genetic testing of prostatectomy specimens was performed to identify the presence of gene mutations. Results The typical IDC-P was diagnosed in two of the 98 patients. The Gleason score of background prostate cancer (PCa) was 4+5 and 4+4. Genetic testing revealed several mutations in DNA repair-related genes, such as <i>CHEK2, FANCC, TOE1, RECQL, USG2A</i>, and <i>PRPF31</i>. The pathological significance of these mutations has conflicting interpretations, as referenced in the ClinVar. Conclusions IDC-P cases can be identified from past HGPIN cases, and cases with genetic abnormalities of conflicting pathological significance can be efficiently detected. Accurate diagnosis of IDC-P enables early intervention with precision medicine for PCa. It is useful to pay attention to HGPIN cases to avoid missing true IDC-P.