Endocrine Abstracts

Objectives: In the personalized medicine era, application of multi-gene Next Generation Sequencing (NGS) panels may be used to analyze plasma circulating tumoral DNA (ctDNA) obtained by liquid biopsies of tumor patients improving management of patients undergoing targeted therapy. This analysis may identify genetic alterations responsible for response and/or resistance during target therapy and may be useful in identifying other biomarkers. Aim of this study was to evaluate the clinical relevance of NGS analysis of ctDNA in patients affected by sporadic Medullary Thyroid Carcinoma (sMTC) during systemic therapy with kinase inhibitors.

Methods: We studied 8 multi-metastatic sMTC patients harboring either RET (n = 7) or HRAS (n = 1) mutations in tumoral tissue. All patients were treated with iRET selpercatinib (n = 6) or multi-kinase inhibitors (MKI) (n = 2), and 4 patients were treated with selpercatinib after progression during previous treatment with (MKI). All patients showed stable disease during therapy. Plasma samples were collected in 4 time-points before therapy start and during follow-up; ctDNA was obtained from 4ml of plasma and analyzed using the Oncomine Pancancer Cell-free DNA NGS panel (Thermo Fisher) that covers mutations and gene fusion in 52 cancer genes. Mutation allele frequency (AF) of mutations were correlated to the status of disease.

Results: Good quality data were obtained from all ctDNA samples reaching limit of detection (LoD) values up to 0.1%. The driver mutation was detected in 5/8 RET-positive patients and AF values dropped during therapy showing a good correlation with disease status and serving as additional biomarker for disease monitoring. In the plasma of patient harboring a HRAS K117N non-hotspot mutation in tissue, we found a mutation in exon 5 of the Estrogen Receptor type 1 (ESR1) with AF=35%; the same mutation was confirmed as somatic in the tumoral tissue. Moreover, the same ESR1 mutation was detected at low AF in the ctDNA of other 2 patients suggesting that it was acquired during tumoral progression. Additional pathogenic mutations in TP53 and GNAS, not previously detected in tumoral tissue, were detected at low AF in plasma of other 3 patients suggesting the presence of other subclones that may emerge during treatment.

Conclusions: These data show that multi-gene combined DNA/RNA panels can be useful to monitor treatment response with kinase inhibitors also in advanced sMTC. While the driver mutation AF correlated with disease status, emergence of additional genetic biomarkers may contribute to disease progression and could provide additional actionable alterations for targeted therapies.