Cancer is one of the major heterogeneous disease with high morbidity and mortality with poor prognosis. Elevated levels of reactive oxygen species (ROS), alteration in redox balance, and deregulated redox signaling are common hallmarks of cancer progression and resistance to treatment. Mitochondria contribute mainly in the generation of ROS during oxidative phosphorylation. Elevated levels of ROS have been detected in cancers cells due to high metabolic activity, cellular signaling, peroxisomal activity, mitochondrial dysfunction, activation of oncogene, and increased enzymatic activity of oxidases, cyclooxygenases, lipoxygenases, and thymidine phosphorylases. Cells maintain intracellular homeostasis by developing an immense antioxidant system including catalase, superoxide dismutase, and glutathione peroxidase. Besides these enzymes exist an important antioxidant glutathione and transcription factor Nrf2 which contribute in balancing oxidative stress. Reactive oxygen species–mediated signaling pathways activate pro-oncogenic signaling which eases in cancer progression, angiogenesis, and survival. Concomitantly, to maintain ROS homeostasis and evade cancer cell death, an increased level of antioxidant capacity is associated with cancer cells.