Utility of circulating tumoral DNA analysis by multi-gene NGS panels in tracking therapy progression of advanced sporadic medullary thyroid carcinoma

BackgroundThe use of multi-gene Next Generation Sequencing (NGS) panels enables monitoring during targeted therapy in tumor patients analyzing circulating tumoral DNA (ctDNA) and thus uncovering genetic changes that may serve as additional biomarkers or influence resistance to therapy. This study aimed to assess the clinical significance of ctDNA NGS analysis in 13 subjects affected by advanced metastatic sporadic Medullary Thyroid Carcinoma (sMTC) undergoing kinase inhibitors therapy.MethodsThe 13 subjects studied, carried either RET (n=12) or HRAS (n=1) driver mutations in tumor tissue and were treated with multi-kinase inhibitors (MKI) (n=2) or RET inhibitor selpercatinib (n=11) either in 1st or 2nd line. At the end-point, all subjects showed response to therapy and stable disease. A 4 time points ctDNA analysis before initiating therapy and during follow-up was performed using the Oncomine Pancancer Cell-free DNA NGS (Thermo Fisher), and mutation allele frequency (AF) was correlated with disease status.ResultsHigh-quality data with limit of detection (LoD) values as low as 0.1% were obtained. Among RET-positive subjects, the driver mutation was identified in 10/12 cases, and AF values strongly correlated with disease status. In a subject harboring a HRAS K117N non-hotspot mutation in tissue, we detected an unexpected variant in exon 5 of Estrogen Receptor type 1 (ESR1) with AF=35% subsequently confirmed as somatic in the tumor tissue. The same ESR1 mutation was identified at a low AF in the ctDNA of two other subjects, suggesting its acquisition during tumor progression. Additionally, we identified pathogenic low AF mutations in RET, HRAS TP53 and GNAS, not previously detected in tumor tissue, in plasma of 10/13 subjects, suggesting a significant presence of other subclones that may be crucial for tumoral resistance and progression.ConclusionsNGS multi-gene panels can be beneficial in tracking treatment response in advanced sMTC and driver mutation AF may serve as biomarker to monitor disease status. The appearance of supplementary genetic biomarkers could play a role in disease advancement and may offer additional actionable alterations for therapies.Legal entity responsible for the studyR. Elisei.FundingPNRR - M4.C2 - Progetto Partenariato Esteso 6 – HEAL ITALIA - CUP I53C22001440006 - Spoke n. 8 (European Union); Thermo Fisher Scientific.DisclosureR. Elisei: Financial Interests, Personal, Invited Speaker: Eisai, Ipsen, Lilly, Bayer. All other authors have declared no conflicts of interest.