Arnold et al. observed in non-small cell lung cancer cells and embryonic stem cells that after ACO2 disruption, cells transitioned from canonical mitochondrial TCA cycle metabolism to non-canonical TCA cycle metabolism mediated by a cascade involving the mitochondrial transporter SLC25A1, ATP citrate lyase (ACL), and malate dehydrogenase (MDH) (Arnold et al., 2022). This evidence concerns the gene MDH2 and small cell lung carcinoma.