Fig. 1.

Key internal sources of reactive oxygen species (ROS) include mitochondria, peroxisomes, endoplasmic reticulum (ER) stress, nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase, and various metabolizing enzymes. External sources such as radiation and xenobiotics also contribute to ROS production. These ROS play a critical role in the initiation and advancement of cancer, impacting the development and progression of the disease. The figure has been reproduced with the permission from Ref. [17]. Copyright 2021 by the authors. Licensee MDPI, Basel, Switzerland.