Abstract P2-23-17: Programmed death ligand-1 expression in triple-negative breast cancer from Nigeria

Abstract

Abstract Introduction: The incidence of triple negative breast cancer (TNBC) in West Africa appears to mirror the higher incidence of the disease among African American women in the United States. However, there remains a paucity of molecular data on TNBC from sub-Saharan Africa, despite the emergence of effective immunotherapies. Methods: Consecutive patients diagnosed with invasive breast cancer between March 2018-Jan 2020 were identified from a prospective clinical database and paired biobank at Obafemi Awolowo University Teaching Hospital (OAUTH). All specimens were processed and fixed in formalin within 60 minutes of excision by a trained pathologist. Tissue sections (4μm thick) representative of tumor were selected for routine evaluation of estrogen, progesterone and human epidermal growth factor receptor-2 expression by immunohistochemistry. This was performed at OAUTH with adequate controls according to the ASCO/CAP guidelines and verified at an outside institution for quality assurance. Additional sections from the FFPE blocks of TNBC specimens were further stained using the Dako PharmDx 22C3 PD-L1 commercial assay according to manufacturer protocols at Dalhousie University. External on-slide controls included tonsil, PD-L1 negative TNBC, and PD-L1 positive TNBC. PD-L1 expression was scored using the combined positive score (CPS), which is the number of 22C3 staining tumour cells, lymphocytes, and macrophages divided by the number of viable tumour cells, multiplied by 100. The threshold for a positive result was a CPS of ≥10 as per manufacturer instructions and institutional protocol. Research ethics board approval as well as data and material transfer agreements between institutions was obtained for this study. Results: From 85 cases, 32 were TNBC (37.6%). The mean age and BMI were 49.6±SD 7.7 and 26.2±5.7, respectively. The majority of patients presented with locally advanced disease (64.2% Stage III, 14.2% Stage IV). Seventy-nine percent (78.5%) of patients received an average of five cycles of neoadjuvant chemotherapy (SD 2.3). From 32 TNBC specimens, 27 had available FFPE tissue blocks, and of those, 24 had interpretable PD-L1 IHC for inclusion in the analysis. A total of 37.5% (9/24) of cases demonstrated a CPS ≥10. Conclusions: Over a third of breast cancer specimens in this Nigerian cohort were triple negative, 37.5% of which had PD-L1 CPS scores of ≥10. These results suggest a large proportion of patients in Nigeria may benefit from access to immunotherapy. This is the first reported incidence of PD-L1 expression in breast cancer from sub-Saharan Africa. Citation Format: Olalekan Olasehinde, Funmilola Wuraola, Aleksandra Kajetanowicz, Gilllian Bethune, Marcia Edelweiss, Peter Ntiamoah, Oluwole Odujoko, Avinash Sharma, Victoria Mango, Peter Kingham, Olusegun Alatise, Gregory Knapp. Programmed death ligand-1 expression in triple-negative breast cancer from Nigeria [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-23-17.