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

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.

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

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.

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.

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.