PROGRAMMED CELL DEATH LIGAND 1 (PD-L1) EXPRESSION IN TRIPLE NEGATIVE BREAST CANCER CASES IN BENIN CITY.

Background: Triple-negative breast cancers (TNBC) have been particularly challenging to manage due to their lack of intrinsic cellular receptors, with the resultant relatively higher morbidity and mortality. Recently, the programmed cell death 1/programmed cell death ligand 1 (PD-1/PD- L1) immune checkpoint pathway has become the focus of immunotherapy, especially for TNBCs. This study aimed to determine the pattern of expression of PD-L1 in TNBC cases in Benin City.

Methods: It was a 3-year retrospective study that involved the PD-L1 immunostaining of the TNBC cases that were diagnosed in the Department of Anatomical Pathology, University of Benin Teaching Hospital, Benin City, from January 1, 2017 to December 31, 2019.

Result: Ninety-two cases of TNBC were tested for PD-L1 expression. Thirteen (14.1%) of the TNBC cases were PDL1 positive to varying degrees on tumour and immune cells. Diffuse tumoural PD-L1 staining was seen in 4 (30.8%) of the PD-L1 positive cases. PD-L1 expression was significantly associated with increasing age up to the fifth decade (p =0.030). All the PD-L1 positive TNBC were invasive breast carcinoma of no special type and mostly grade 2 tumours; however, there was no significant association between PD-L1 expression and histological subtype or grade.

Conclusion: PD-L1 expression was shown to occur at a relatively low rate among TNBC cases in this environment and was significantly associated with increasing age. This study has shown that 14.1% (1 in 7) of our TNBC patients could benefit from immune checkpoint inhibitor therapy.