Background: Triple-negative breast cancer (TNBC) has a different epidemiology, histologic features, and clinical behavior, and lacks effective targeted therapies that can improve the benefits gained from chemotherapy compare to other subtypes. Several pathways associated with the retinoblastoma protein (pRB) are perturbed in this aggressive breast cancer.

Objective: To investigate the prevalence of pRB loss among Thai patients with TNBC and to compare clinical outcomes between patients with and without pRB expression.

Materials and Methods: The pRB status was evaluated by immunohistochemistry in 71 patients who were diagnosed with TNBC. The clinicopathologic features and the association between pRB expression and clinical outcomes were analyzed retrospectively.

Results: The prevalence of pRB loss was 63.4% (45 out of 71). No differences were observed in the patients and/or tumors characteristics in terms of pRB expression, but there was a trend toward a high frequency of high Ki-67 expression in pRBnegative tumors (88.9% versus 73.3%, 2P=0.052). However, the differences between two groups were not statistically significant. After a median follow-up of 67.7 months, 5-year disease free survival estimates were 73% and 65% (2P=0.610) and 5-year overall survival estimates were 76% and 65%, (2P=0.500) in patients with pRB loss and with pRB-positive tumors, respectively. According to multivariable Cox proportional hazards models, pRB expression did not independently correlated with DFS or OS in cases of TNBC (HR 1.32, 95% CI 0.56 to 3.13, 2P=0.530; for DFS and HR 1.19, 95% CI 0.49 to 2.9, 2P=0.710; for OS).

Conclusion: The prevalence of RB loss in Thai women with TNBC was significantly higher than in previous studies. RB loss was associated with more aggressive behavior; however, it did not translate into inferior survival outcomes.

Keywords: Retinoblastoma protein, Triple-negative breast cancer