CLINICAL SIGNIFICANCE OF PD-L1 EXPRESSION IN PARATHYROID CANCER

Introduction. Parathyroid carcinoma accounts for 0.5% to 5% of all cases of primary hyperparathyroidism and it is an exceedingly rare endocrine malignancy first described in 1933. Most experts recommend en bloc excision at initial surgery as the only chance for its cure. Both chemotherapy and radiotherapy have not been demonstrated to be beneficial in parathyroid carcinoma. Some patients have multiple recurrences or metastases. Therefore, new therapies are urgently needed. Inhibition of the interaction between Programmed Death Receptor 1 (PD-1) and Programmed Death Receptor Ligand 1 (PD-L1) enhances T-cell responses in vitro and mediates clinical antitumour activity. Aim. We analysed the expression of PD-L1 in parathyroid cancer to evaluate its potential as target for immunotherapeutic strategy. Subjects and methods. A cohort of 18 patients were diagnosed with primary or metastatic parathyroid cancer. Immunohistochemistry was performed in 18 formalin-fixed paraffin-embedded specimens using a rabbit monoclonal antibody. A 5% cut-off value was applied for PD-L1 positivity. Results. The anti PD-L1 antibody showed a predominantly membranous staining pattern in parathyroid cancer cells. Programmed Death Receptor Ligand-1 expression was found in 22.2% of all parathyroid carcinoma cases. There was no correlation between the expression of PD-L1 with lymph node metastasis, gender and age (P>0.05). Conclusion. This expression of PD-L1 in human parathyroid cancer suggests that patients with parathyroid cancer could profit from immunotherapeutic strategies using anti-PDL1 antibodies.