Mitochondria, cellular powerhouses, play a central role in apoptosis. In addition, they are suspected to contribute to aging. There is also increasing evidence that abnormalities in mitochondrial function help cancer development. Changes in mitochondrial transcription and oxidative phosphorylation pathways are observed in many types of cancer. Somatic mutations and quantitative changes in mitochondrial DNA were found in tumors, suggesting that alterations in mitochondrial DNA and the resulting respiratory deficiency play a role in carcinogenesis. It was postulated they could be useful as cancer markers. Mitochondria with abnormal functions are suitable targets for anticancer drugs.