Genomic profile of Japanese patients with rare ductal adenocarcinoma of the prostate has high grade and poor prognostic aspects.

e17046 Background: Ductal adenocarcinoma (DAC) is a rare subtype of prostate cancer with unknown etiology and poor prognosis. Genomic profile analysis using next-generation sequencing has the potential to elucidate the pathogenesis of rare cancers. To date, some studies have investigated the genetic profile of the DAC genotype; however, no definitive findings have been obtained due to the small number of patients and limited geographic coverage. The discovery of novel prognostic biomarkers and identification of new pharmacotherapeutic targets for DAC are currently of research interest. The aim of this study is to analyze the genomic profile of DAC in a Japanese population and to summarize its features. Methods: Clinical and histopathological records from our three hospitals were searched for radical prostatectomy, transurethral resection of the prostate, and prostate needle biopsy specimens containing a DAC component in the past 10 years. Twenty-eight patients diagnosed with DAC of the prostate were identified, of whom 15 were eligible for genomic profile analysis and 10 patients (66.7%) had the pure type. Genomic evaluation was performed using either the FoundationOne CDx or PleSSision testing platform. Results: At least one genomic alteration occurred in 14 patients (93.3%), and the most frequently mutated gene was tumor suppressor protein p53 ( TP53), which was found in seven cases (46.7%). Additionally, five cases (33.3%) had mutations in retinoblastoma transcriptional corepressor 1 ( RB1), and all these patients had the pure type. Four cases had both TP53 and RB1 alterations, and most of these possessed the pure type and had PSA levels of less than 4.0. Compared to previous study results, the frequency of genetic alterations in the phosphoinositide 3-kinase (PI3K) pathway (n = 3; 20.0%) and Wnt-β/catenin pathway (n = 6; 40.0%) was comparable, but alterations in the DNA damage repair (DDR) pathway were few (n=1; 6.7%). None of the patients presented high tumor mutation burden or microsatellite instability. Conclusions: We found that the Japanese cohort with DAC has unique features such as high frequency of alterations in tumor suppressor gene such as TP53 and RB1, and few DDR pathway alterations, suggesting the existence of regional and racial differences in genomic profiles. Genomic analysis using next-generation sequencing is expected to be useful in elucidating the pathogenesis of DAC, and further accumulation of cases is considered important.