Nearly Half of Patients with Anaplastic Thyroid Cancer May Be Amenable to Immunotherapy.

[IMPORTANCE] Poorly differentiated cancer (PDC) and anaplastic thyroid cancer (ATC) have an aggressive course of disease with limited treatment options. The expression of programmed cell death ligand-1 (PD-L1) has been used to determine the responses of many cancers to immunotherapy. The aim of the study was to investigate the expression of PD-L1 in a cohort of patients with PDC and ATC to assess their suitability for immunotherapy. Data, settings, and participants: This study is a retrospective cohort review of patients treated for PDC and ATC treated at a tertiary referral institution during the period 2000-2020. PD-L1 22C3 pharmDx qualitative immunohistochemistry was performed on formalin-fixed, paraffin-embedded (FFPE) specimens of tumours to detect the presence of the PD-L1 protein.

[MAIN OUTCOME MEASURES] The percentage of tumours that were positive for PD-L1 immunohistochemistry and the PD-L1 protein expression as measured by using the Tumour Proportion Score (TPS). Secondary outcomes studied were the associations between demographic, clinicopathological, treatment and disease outcomes and PD-L1 expression.

[RESULTS] Nineteen patients (12F:7M) with a mean age of 65.4 (±14.3 SD) years were diagnosed with PDC in 4 (21%) and fifteen were diagnosed with ATC (79%) during the study period. Fifteen (79%) patients underwent some form of surgery, with R0 resection achieved in only three of the fifteen (20%) patients. Overall, PD-L1 expression was seen in seven of the fifteen (47%) of the patients with ATC, with no positivity seen in the patients with PDC. PD-L1 expression had no impact on treatment modality and positive expression was not significantly associated with stage of disease, metastasis, or survival.

[CONCLUSION] Nearly half of patients with ATC express PD-L1 and may be amenable to immunotherapy with pembrolizumab.