INCIDENCE, PROGNOSTIC AND PREDICTIVE SIGNIFICANCE OF PROGRAMMED DEATH LIGAND-1 (PD-L1) IN THYROID CARCINOMA OF FOLLICULAR CELL ORIGIN anjali@sgpgi.ac.in

396-05

INCIDENCE, PROGNOSTIC AND PREDICTIVE SIGNIFICANCE OF PROGRAMMED DEATH LIGAND-1 (PD-L1) IN THYROID CARCINOMA OF FOLLICULAR CELL ORIGIN

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India

Oral or Poster

Programmed Death Ligand-1 (PD-L1) expression in thyroid cancers (TC) could predict response to immune check point inhibitor (ICI) therapy and may have prognostic value. The primary objective of this study was to investigate the incidence of PD-L1 expression in TC and secondary objectives were to corelate PD-L1 expression with various clinicopathologic prognostic factors including BRAFV600E expression and tumor infiltrating lymphocytes (TIL).

Retrospective study (2004-2019) consisting of 247 TC patients including 169 papillary, 57 follicular, 18 poorly differentiated and 3 Hurthle cell carcinoma. Pathology was reviewed and immunohistochemistry staining for PD-L1 and BRAFV600E performed. PD-L1 expression was correlated with clinicopathologic prognostic factors disease-free survival (DFS) and overall Survival (OS).

The overall incidence of PDL-1 immunostaining was 28.3% and didn’t differ significantly by histology type (p=0.255). PDL positive tumors showed significantly high incidence of BRAF immunostaining (81.4 Vs 33.3%; p=<0.0001) but significantly low TIL (61.4 Vs 92.1%; p=0.0001). At different cut offs, PDL-1 expression was significantly associated with age (p=0.043), sex (p=0.024) and tumor multicentricity (p=0.046) but not with tumor size (p=0.580), lymph node metastases (p=1.000), extra-thyroidal invasion (p= 0.691), distant metastases (p=0.847), Neutrophil- Lymphocyte Ratio (p=0.322), and Platelet-Lymphocyte Ratio ratio (p=0.130). DFS (p=0.509) and OS (p=0.861) for the whole cohort as well as for different histology were not significantly affected by PDL-1 expression.

The incidence of PDL-1 expression does not vary significantly in different TC. The concurrent expression of PDL-1 with BRAF could potentially indicate use of dual target therapy in radioiodine refractory TC.