RF11 | PSAT272 Suppressive Tumor Immune Microenvironment is Associated with Aggressive Differentiated Thyroid Cancer

BACKGROUND: The incidence of differentiated thyroid cancer (DTC) has tripled over the last 30 years in the US. While most patients respond to conventional treatment, some have an aggressive course with a dismal 5-year survival of 15.3%. There is a need to identify novel markers in addition to clinico-pathologic criteria to better prognosticate DTC patients. In addition, exploration of immunotherapies in advanced DTC underlies the critical need to investigate the immune interface of DTC to identify potential therapeutic targets and those likely to respond to immunotherapies. AIMS: We aimed to identify tumor-infiltrating immune cells and checkpoints [programmed cell death protein 1 (PD-1) and its ligand (PD-L1)] associated with DTC and investigate their association with metastatic and advanced DTC. METHODS: We performed multiplex immunofluorescence on de-paraffinized thyroid tissue collected at initial thyroidectomy from 17 adults with DTC. We identified cell-surface molecules to characterize the tumor immune microenvironment for leukocytes (CD45+), T cells (CD3+), B cells (CD19+), natural killer cells (CD56+), T regulatory cells (CD3+FOXP3+), CD4+ T cells (CD3+CD4+), CD8+ T cells (CD3+CD8+), macrophages (CD68+), M2 macrophages (CD68+CD163+), and immune checkpoints PD-1 and PD-L1. Tonsil tissue was used as positive control. Immunofluorescence staining was quantified by cell counting HALO software. We compared the mean percentage expression of immune markers between tumor and adjacent thyroid tissue from the same patient by paired t-test, and in exploratory analysis between intra-tumoral tissue in patients with versus without distant metastases by student's t-test; p value<0.05 was used for significance. RESULTS: Overall, in 17 DTC patient samples, most leukocyte infiltrate occurred along the leading edge of the tumor and in the peritumoral thyroid tissue. Immune checkpoints PD-1 and PD-L1 were highly expressed in the tumor as compared to adjacent thyroid tissue (p<0.05). A higher trend for M2 macrophages was observed in the tumor but was not statistically significant. Intra-tumoral expressions of T regulatory cells, macrophages and PD-L1+ cells were more in samples for DTC patients with metastases (n=3) as compared to those without (n=14). CONCLUSIONS: Immune profiling demonstrated significant differences between tumor and adjacent thyroid tissue, particularly for PD-1 and PD-L1, indicating their role in DTC occurrence. Intra-tumor infiltration of T regulatory cells, macrophages and PD-L1+ cells was more in metastatic DTC indicating their potential role in aggressive behavior of DTC. These data suggest that suppressive tumor immune microenvironment portends more aggressive behavior of DTC, and that specific immune suppressive markers may be potential therapeutic targets. We are continuing to expand our sample size to have adequate power for comparing groups with various clinico-pathologic severities and analyzing the role of pro-tumoral M2 macrophages in DTC prognosis. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Saturday, June 11, 2022 1:36 p.m. - 1:41 p.m.