Study of PD-L1 Expression in Papillary Thyroid Carcinoma and its Correlation to the Clinico-Pathological Characteristics

Abstract

Abstract Background Thyroid carcinoma is the most common endocrine malignancy, diagnosed annually worldwide. Papillary thyroid carcinoma (PTC) is the most common histologic subtype of thyroid carcinoma, accounting for around 90% of new cases. The expression of PD-L1 is investigated as a potential prognostic and predictive biomarker of the clinical outcome. Aim of the Work The study aimed at assessing PD-L1 expression in patients with PTC and its variants, also to determine its correlation with clinico-pathological parameters. Patients and Methods This is a cross-sectional study conducted on 50 patients diagnosed with PTC and treated at the Head and Neck Clinic, Ain Shams University Hospitals in the period from 2020-2022. Results We assessed the PD-L1 status by immunohistochemistry on formalin fixed and paraffin embedded surgical tissues of 50 patients diagnosed with PTC and its variants. Monoclonal Mouse anti-Human PD-L1 clone 22C3 from Dako Company was used to detect the PD-L1 status in tumor cells using the clone 22C3. PD-L1 positive expression was detected in 16/50 patients (32%) at a 1% threshold. The clinico-pathologic factors over a median duration of 17 months was studied and its correlation with the PD-L1 status. The mean age of the study population at diagnosis was 43 years with 92 % of cases were female patients. All patients underwent total thyroidectomy with 21 patients underwent lymph node dissection. The most common stage was stage I, and the most common histopathologic subtype was the classical PTC subtype. Most of the study population received radioactive iodine (84%). Median disease free survival was not reached as only 7 patients developed recurrence in the follow up period. In our study, statistically significant correlation was found between patients with PD-L1 positive tumor cells and higher T stage (p = 0.021), and positive pathological lymph nodes (p = 0.01). All the 16 patients who were found to have PD-L1 positive expression, received RAI (p = 0.034). Whereas no association was found with age (p = 0.197), sex (p = 0.584), multifocality (p = 0.566), lymphovascular invasion (p = 0.061), extra-thyroid extension (p = 0.725), thyroiditis (p = 0.135), histological variants (p = 0.520), margins (p = 0.410), post-operative thyroglobulin (p = 0.120), and disease free survival (p = 0.239). Conclusion PD-L1 expression correlates with T stage and pathological lymph nodes and may be used as a prognostic marker for PTC patients. Further follow up needs to be done to confirm the prognostic value of PD-L1 expression in PTC.