<jats:sec> <jats:title>BACKGROUND:</jats:title> <jats:p>Anaplastic thyroid cancer (ATC) is an aggressive malignancy without effective treatments. ATC cells demonstrate upregulated glycolysis (Warburg effect), generating lactate that is subsequently exported by monocarboxylate transporter 4 (MCT4). This study aims to determine whether MCT4 inhibition can suppress ATC growth.</jats:p> </jats:sec> <jats:sec> <jats:title>STUDY DESIGN:</jats:title> <jats:p>ATC cell lines 8505C, JL30, and TCO1 were grown in low (3 mmol/L; LG) or high (25 mmol/L; HG) glucose medium containing the lactate shuttle inhibitors acriflavine (10–25 μmol/L; ACF), syrosingopine (100 µmol/L; SYR), or AZD3965 (20 µmol/L; AZD). Lactate level and cell proliferation were measured with standard assays. Seahorse analysis was performed to determine glycolytic response.</jats:p> </jats:sec> <jats:sec> <jats:title>RESULTS:</jats:title> <jats:p>Compared with HG, addition of ACF to LG decreased lactate secretion for both 8505C (p < 10<jats:sup>-5</jats:sup>) and JL30 (p < 10<jats:sup>-4</jats:sup>) cells, whereas proliferation was also reduced (p < 10<jats:sup>-4</jats:sup> and 10<jats:sup>-5</jats:sup>, respectively). During Seahorse analysis, addition of oligomycin increased acidification by 84 mpH/min in HG vs 10 mpH/min in LG containing ACF (p < 10<jats:sup>-5</jats:sup>). Treatment with LG and SYR drastically diminished 8505C and TCO1 growth vs HG (p < 0.01 for both). LG and AZD treatment also led to reduced proliferation in tested cell lines (p ≤ 0.01 for all) that was further decreased by addition of ACF (p < 10<jats:sup>-4</jats:sup> vs HG, p ≤ 0.01 vs LG and AZD).</jats:p> </jats:sec> <jats:sec> <jats:title>CONCLUSION:</jats:title> <jats:p>Inhibition of lactate shuttles significantly reduced proliferation and glycolytic capacity of ATC cells in a low-glucose environment. Targeting suppression of glycolytic and lactate processing pathways may represent an effective treatment strategy for ATC.</jats:p> </jats:sec>