MT-ND6 and breast cancer: We and others previously showed that certain mitochondrial DNA (mtDNA) somatic mutations or single nucleotide variants (SNVs) enhanced the invasion and metastasis of mouse and human cell lines, e.g., NADH dehydrogenase subunit 6 (ND6) G13997A in Lewis lung carcinoma cells [1, 2], ND6 13885insC in mouse fibrosarcoma cells [1, 2], ND3 G10398A and tRNALeu(CUN) A12308G in human breast cancer cells [3, 4], ATP6 T8993G and ND3 A10398G in human prostate cancer cells [5, 6], tRNALeu(CUN) A3243T in human osteosarcoma cells [7] and 12S rRNA (RNR1) G709A in human hepatocellular carcinoma [8].