Expression of PD-L1 using SP142 CDx in triple negative breast cancer

Triple negative breast cancer (TNBC) represents a small subtype of breast cancer yet it has the worst outcome. Immunotherapy using immune checkpoint inhibitors combined with chemotherapy was recently approved by the FDA raising the hope for an improved outcome. The approval was based on demonstration of a positive PD-L1 expression using the SP142 CDx assay ¹. We aimed to study a cohort of TNBC patients in terms of prevalence of the PD-L1 expression using the approved assay and to investigate its association with clinicopathological variables. This is a single center retrospective study consisting of 49 TNBC patients who had available archived paraffin-embedded tissue blocks from the primary tumors. All blocks were stained using the SP142 CDx assay as per the manufacture's instruction. Clinicopathological data were collected from medical records. Eighteen of the 49 (36.7%) patients were found to have a score of 1% or more by the immune cell-scoring algorithm. PDL-1 expression was significantly associated with the degree of tumor infiltrating lymphocytes (TILs). No additional significant relationship was found between PD-L1 expression and any of the other investigated clinicopathological variables. Although a trend of favorable prognostic association with PD-L1 expression was noted. The overall and event free survival were significantly related to pathological response to neoadjuvant therapy. Conclusion: Our PD-L1 rate of 36.7% is close to the results of the previously reported 40.9% in the IMpassion 130 trial. There were no significant association between positive PD-L1 expression and clinicopathological variables however a trend of a favorable outcome was observed.