Abstract
Abstract Programmed cell death ligand 1 (PD-L1) has been shown to induce potent T-cell mediated anti-tumoral immunity. The significance of PD-L1 expression on prognosis of breast cancer remains controversial and its prevalence and prognostic value in breast cancer from Middle Eastern ethnicity is lacking. A total of 1003 unselected Middle Eastern breast cancers were analyzed for PD-L1 expression using immunohistochemistry. The association with clinico-pathological markers and impact on overall survival as well as recurrence free survival was determined. PD-L1 expression was seen in 32.8% (329/1003) cases. PD-L1 positivity was significantly associated with poor prognostic indicators such as younger patients (p = 0.0499), high grade tumors (p = 0025), ER negative (p < 0.0001) and PR negative (p = 0.0001) status as well as high Ki-67 index (p < 0.0001). We also found a significant association between PD-L1 expression and deficient mismatch repair protein expression (p = 0.0009). No association was found between PD-L1 expression and clinical outcome. However, on further subgroup analysis, PD-L1 expression was found to be an independent marker for favorable prognosis in triple negative breast cancer (TNBC) (Hazard ratio = 0.27; 95% confidence interval = 0.10 - 0.63; p = 0.0018). In conclusion, we demonstrated strong association between PD-L1 and MSI in Middle Eastern BC patients and showed that PD-L1 overexpression on tumor cells was an independent favorable prognostic factor in TNBCs from this ethnicity. Overall, these findings might help in the development of more appropriate treatment strategies for BC in Middle Eastern population. Citation Format: Khawla S. Al-Kuraya, Abdul K. Siraj, Sandeep K. Parvathareddy, Saeeda Ahmed, Allianah Benito, Kaleem Iqbal. PD-L1 protein expression in Middle Eastern breast cancer predicts favorable outcome in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3190.
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