MON-379 Vitamin D Signaling Expression Markers in Thyroid Tumors

Abstract Disclosure: R. Conard: None. J. Lin: None. B.R. Haugen: Veracyte, Inc. M. Alshalalfa: Veracyte, Inc. H. Yangyang: Veracyte, Inc. J.P. Klopper: Veracyte, Inc.. W.S. Goldner: None. Introduction: Vitamin D receptor (VDR) expression and the relative synthesis and catabolism of vitamin D (VD) appears to play a role in tumor growth regulation. The aim of this study was to characterize VDR, VD regulatory enzymes, and VD pathway target gene expression in thyroid nodules sent for Afirma Genomic Sequencing Classifier (GSC) molecular testing. Methods: mRNA expression of VDR and genes affecting VD synthesis (CYP27B1 (1α-hydroxylase - generation of active 1,25 VD), CYP27A1 (sterol 27-hydroxlase - conversion of VD to 25,VD), and CYP24A1 (24-hydroxylase - catabolism of 1,25 VD )) were analyzed across 47,695 thyroid nodules ((B)ethesda III-VI cytology). Differential expression of these targets was explored across Afirma benign (GSC-B) and suspicious (GSC-S) categories, cytology group, and relative to the BRAFV600E variant. The expression of VD target genes (CD14, ORM1, CALM, CLMN) was assessed and a VD activity score was derived by averaging the expression level of these targets. Results: 30,259 nodules were GSC-Benign (GSC-B), 15,815 were GSC-Suspicious (GSC-S), and 1,621 were cytologically B V or VI. In GSC-S and BV/VI nodules, VDR expression was lower in nodules with BRAFV600E compared to BRAFwt. CYP27A1 expression was not significantly different from GSC-B levels in any other category. CYP24A1 expression was higher in GSC-S compared to GSC-B, and in B V/VI nodules, and higher still in BRAFV600E compared to BRAFwt subgroups. CYP27B1 expression was lower in GSC-S and BV/VI nodules compared to GSC-B nodules and even lower in BRAFV600E mutant GSC-S and BV/VI nodules compared to those with BRAFwt. The same pattern was seen for each VD signaling target gene. The novel VD activity score followed the same pattern, with the lowest levels in samples with BRAFV600E. Samples with RAS like alterations (RAS family and PAX8-PPARy fusion) had a VD activity score lower than GSC-B and higher than those with BRAFV600E. Additionally, the VD activity score was strongly positively correlated with VDR expression (r=0.45) and strongly negatively correlated with ERK activity (r= -0.48). Conclusion: Cytologically indeterminate thyroid nodules with suspicious GSC results and malignant nodules appear to have reduced VD signaling. This VD signaling is further diminished in the presence of BRAFV600E and to a lesser extent, RAS like alterations. Similarly, the novel VD activity score we developed is lower in molecularly suspicious nodules and those with high-risk molecular variants and fusions. The VD activity score is also negatively correlated with ERK signaling, a marker of MAPK signaling and tumor aggressiveness. It is possible the VD activity score could serve as a preoperative marker that may modify prognosis in the absence of variants and fusions correlated with low or high-risk tumors, or in the presence of intermediate risk mutations. Presentation: Monday, July 14, 2025