New insight on the biological role of p53 protein as a tumor suppressor: re-evaluation of its clinical significance in triple-negative breast cancer.

While p53 mutation is found in the majority of triple-negative breast cancer (TNBC) and despite recent developments in p53-targeting agents, their therapeutic application is still limited by the absence of standard biomarkers and ambiguousness of its essential biological role in cancer. Whole sections from 305 TNBC cases were stained for p53 to determine the correlation with lymph node metastasis and clinical outcomes in the whole cohort as well as in stratified patient groups according to AJCC stage and the use of adjuvant chemotherapy. Reduced immunohistochemical expression of p53 was an independent risk factor for lymph node metastasis. p53 overexpression was predictive of better clinical outcome in all patients (P = 0.012, disease-free survival and P = 0.008, overall survival) and the stratified cohorts of those who had early breast cancer and received adjuvant chemotherapy. Suppression of endogenous mutant p53 by siRNA and induction of wild-type p53 repressed TNBC cell invasion in vitro. In TNBC, increased immunohistochemical expression of p53 may reflect the accumulation of wild-type p53 rather than the mutant form. Strong p53 protein expression may serve as a favorable prognostic indicator and provide evidence for the use of specific agents targeting p53.