Leucine Zipper-EF-Hand Containing Transmembrane Protein 1 (Letm1) is encoded by the Letm1 gene, which is a transmembrane protein located in the inner membrane of mitochondria and functions as a Ca2+/H+ antiporter.336 In gastric, colorectal, and lung cancer, studies reveal a positive correlation between Letm1 and stemness-related signatures.337–339 Furthermore, suppressing or elevating the Letm1 expression leads to inhibited or enhanced stemness of colorectal cancer or osteosarcoma cells, respectively.340,341. The gene discussed is LETM1; the disease is lung cancer.