One probable explanation for the significant decrease in proliferation in cybrids with benign mitochondria against a metastatic cell nuclear background could be that, in metastatic breast cancer cells, mitochondria-mediated up-regulation of NDRG1 expression enhances lipid uptake by SUM-159 cells, which may promote cell proliferation in these lipid-dependent cell lines. The gene discussed is NDRG1; the disease is breast carcinoma.