Abstract 361P
Background
Ductal adenocarcinoma of the prostate (DCa) is a rare cancer with poor prognosis, but the pathogenesis of DCa has not been elucidated and no useful biomarkers have been established. We reported that genomic profiling of Japanese DCa patients revealed that TP53 and RB1 mutations occur frequently more than western countries and that patients with p53 or RB1 mutations have a worse prognosis than those without mutations. However, due to the limited laboratory facilities and the cost of genomic analysis, it is impractical to analyze all patients. The aim of this study was to investigate the usefulness of p53 immunohistochemistry (IHC) staining as a surrogate prognostic biomarker in DCa.
Methods
We included 21 of 30 patients diagnosed with DCa at our institutions past 15 years. Formalin-fixed paraffin-embedded sections were subjected to p53 IHC staining, and abnormal staining pattern of p53 were classified by dedicated uropathologist as overexpression, null mutant, or cytoplasmic expression. Genomic profiling was performed using FoundationOne CDx or PleSSision testing platform. The correlation between the results of each method was analyzed.
Results
Ten patients (47.6%) had pure type cancer, while 11 patients (52.4%) had a mixed type cancer with acinar adenocarcinoma. The p53 IHC showed 7 cases of overexpression (33.3%), 2 cases of null mutant (9.5%), 0 cases of cytoplasmic expression (0.0%), and 12 cases of wild type (57.2%). Of the 12 cases for which genomic analysis was available, 4 (33.3%) were positive for TP53 mutations, 2 were nonsense mutations and 2 were missense mutations. All 4 mutation-positive cases were classified as overexpression on p53 IHC staining, and all 8 mutation-negative cases were wild type, with a mutation concordance rate of 100%.
Conclusions
Both mutation-positive and mutation-negative predictive value were 100%, indicating that TP53 mutations in Japanese DCa patients can be accurately detected by p53 IHC staining as a surrogate prognostic biomarker. These results suggest that p53 IHC staining may contribute to future multicenter, multi-case studies in terms of simplicity and versatility.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.