The decrease in mtDNA:nDNA ratio was concomitant with sensitization to gemcitabine induced by TK2 siRNA in TK2HIGH (MCF7) cells (Figure 5A), but not A549 cells with low TK2 (Figure 5B), implies that TK2 is critically involved in tumor cell mitochondrial dysfunction and subsequent toxicity in response to combined treatment with TK2 siRNA and gemcitabine in these cells. The gene discussed is TK2; the disease is neoplasm.