PD-1/PD-L1 Expressions in Medullary Thyroid Carcinoma: Clinicopathologic and Prognostic Analysis of Chinese Population

Introduction: Few studies have focused on PD-L1 expression in medullary thyroid carcinoma (MTC). Expressions of PD-1 and PD-L1 and their clinicopathologic and prognostic relevance were therefore further investigated on a relatively large population of MTC patients.

Materials And Methods: Surgical specimens were obtained from 87 MTC patients during a median follow-up of 37.7 months. PD-1 and PD-L1 expressions on tumor and associated immune cells were studied immunohistochemically using >1% positive cells as a threshold for positivity. Their correlations with clinicopathologic and prognostic feature were analyzed.

Results: PD-1 and PD-L1 were positively stained in 22 and 19 MTC patients. Most PD-L1-positive cases (18/19) showed weak to moderate staining intensity. PD-1 and PD-L1 were co-expressed in 11 patients. PD-L1 positivity was significantly correlated with distant metastases at surgery (21.1% vs 1.5%, P = 0.007). Coexpression of PD-1 and PD-L1 in MTC was correlated with advanced pathologic TNM stage III/IV (P = 0.040) and distant metastases at surgery (P = 0.013). However, there was no other clinicopathologic and prognostic relevance regarding to PD-1, PD-L1 or their coexpression in our MTC patients.

Conclusion: PD-1/PD-L1 pathway was expressed in MTC patients and was significantly correlated with the distant metastases at surgery, which may shed light on PD-1/PD-L1 as a promising therapeutic target in MTC. Future better understanding of PD-1/PD-L1 expression and their relationship with immunotherapy response may provide direct evidence for management of refractory MTC.