In the cohort of primary breast tumor specimens – more heterogeneous cell populations – we find a positive but weak correlation (ρ ≤ 0.25) between mtDNA content and ESRP1, SNAI1 and TGFB1. In in vitro studies, a reduction in mtDNA content resulted in decreased ESRP1 protein levels but, contradictory to our findings, increased SNAI1 mRNA expression or TGFB protein expression. This evidence concerns the gene SNAI1 and breast neoplasm.