Immunohistochemistry Expression of Programmed Death-Ligand 1 in Colorectal Carcinoma among Nigerians.

Background: Colorectal carcinoma (CRC) is the most common gastrointestinal malignancy in Nigeria with a dismal 5-year survival rate. Interactions between the CD8+ T-lymphocytes and the immune checkpoints such as cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed death-ligand 1 (PD-L1) expressions are important. Novel antibodies have been developed against these immune checkpoints and have been found to improve clinical outcome in many solid organ malignancies.

Aim: We aimed to determine immunohistochemical expression of PD-L1 in resected CRC cases assembled on tissue microarray blocks.

Methods: Representative blocks and clinical information of resected CRC cases between 2010 and 2019 were retrieved from the archives of our department. Tissue microarray (6 × 4) blocks were constructed with 2 mm core needles. Immunohistochemistry using anti-PD-L1 rabbit monoclonal antibody (clone EPR19759 #213524, 1:200 Abcam, MA, USA) was carried out according to manufacturer's instruction.

Results: The study included 170 cases, of which 144 cases had sufficient tissue for analysis. The peak incidence was observed in the 50-59 age group. Approximately 80.1% of the cases were in T3 and T4 stages. Only 8 (5.6%) out of 144 cases were positive for PD-L1. All the PD-L1 positive cases were either right-sided CRC (6/68) or rectal cancer (2/3). Of the seven positive cases with available histological grading, four were poorly differentiated/mucinous variants and three cases were moderately differentiated.

Conclusion: PD-L1 expression in CRC was low (5.6%) and showed strong associations with higher tumor grades (P < 0.013), right-sided tumors (P < 0.002), and rectal cancer. There was no association with age, tumor stage, and lymph node status.