Williams et al. (1998) reported that Mn-SOD heterozygotes (±) exhibited a 50% decrease in Mn-SOD activity, which was associated with impaired function and increased oxidative stress in the mitochondria in liver cells. Van Remmen et al. (2003) also reported increased and lifelong oxidative damage to DNA in liver, brain, and heart tissues of the Mn-SOD± mice; oxidative damage to DNA was associated with an increased incidence of cancer in these mice. Here, SOD2 is linked to cancer.