Fookerah, Prishila2; Perampalam, Sumathy1,6; Ali, Sayed3,6; Shadbolt, Bruce4,6; Fadia, Mitali5,6
1 Department of Endocrinology, Canberra Hopsital, ACT Australia
2 Department of Medicine, Canberra Hospital, ACT, Australia
3 Department of Oncology, Canberra hospital, ACT, Australia
4 Department of Clinical Epidemiology, Biostatistics and Data Science Canberra Hospital, ACT, Australia
5 Department of Pathology, Canberra Hospital, ACT, Austrlia
6 Medical School, Australian National University, ACT, Australia
Background: The impact of the immune system on disease progression in papillary thyroid cancer (PTC) is poorly understood. PD-L1 expression as a predictor of disease progression has been explored recently with PD-L1 positivity in PTC ranging between 6.1% and 82.5%.However PD-L1 expression may be altered in PTC with concurrent lymphocytic thyroiditis (LT), which has not been accounted for consistently in previous studies (1-5).
Aim: To determine if lymphocytic thyroiditis has an effect on PD-L1 expression in PTC.
Method: A cross sectional study was performed, analysing PTC patients diagnosed from 2005-2012. Immunohistochemistry analysis of archived formalin fixed paraffin embedded thyroid tissues for PD-L1 expression using a rabbit monoclonal anti-PD-L1 antibody (Ventana SP263) was performed. The expression of membranous PD-L1 in thyroid was considered positive and intensity of the staining was scored. The results were classified according to the AJCC TNM staging system comparing samples with and without LT. Chi-square tests were performed for statistical analysis.
Results: The study cohort consisted of 69 PTC cases with 21 (30.4%)cases of LT. Expression of PD-L1 in tumour cells was present in 8(38%) cases with LT and 2 cases (4.1%) without LT (Chi Square =13.6; p=0.0002) . There was no difference in positivity across the TNM stages. High intensity expression of PD-L1 was seen in PTC at lower stage disease with concurrent LT. In LT without PTC, PD-L1 expression was absent in thyroid, but present in lymphocytes.
Conclusion: Frequency of PD-L1 expression was significantly higher in PTC with LT than PTC without LT. PD-L1 expression in PTC may be an epiphenomenon and future studies should account for presence of concurrent LT.
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