Purpose: We aimed to explore the expression of DNA damage response machinery proteins and their integrated prognostic value in different subgroups of breast cancer.
Methods: Expression of NBS1, BRCA1, BRCA2, ATM, and p53 was determined by immunohistochemistry in 419 surgically resected breast tumors.
Results: Loss of NBS1, BRCA1, ATM, and abnormal p53 expression was significantly associated with lower disease-free survival rates. Abnormal DNA damage response protein expression, defined as loss of any one of NBS1, BRCA1, ATM, and/or abnormal p53 expression, was observed in 258 of 399 evaluable cases (64.7%) and was significantly associated with higher tumor grade, larger tumor size, and ER-negative, and/or PR-negative status. Most patients with luminal B (86.1%), HER2-enriched (94.4%), and triple-negative (86.8%) breast cancers had abnormal DNA damage response protein expression. In contrast, abnormal DNA damage response protein expression was found in only 53.8% of luminal A tumors. Abnormal DNA damage response protein expression was associated with significantly lower 5-year disease-free survival rates in all patients (95.6% vs. 84.8%, p = 0.001), as well as in the luminal A subgroup (97.4% vs. 89.0%, p = 0.011). In multivariate analysis, abnormal DNA damage response protein expression remained an independent predictor of shorter disease-free survival for luminal A subtype (hazard ratio 3.14, 95% confidence interval 1.16-8.47; p = 0.024).
Conclusion: Abnormal DNA damage response protein expression is found in most luminal B and HER2-enriched breast cancers as frequently as in triple-negative breast cancer. In the luminal A subtype, abnormal DNA damage response protein expression is an independent prognostic marker.
Keywords: BRCA1 protein; BRCA2 protein; DNA damage; DNA repair; Homologous recombination; Prognosis.