Cancer Prevalence and Etiology in Wild and Captive Animals

Despite the evolution of numerous natural cancer suppressor mechanisms (DeGregori, 2011 ), neoplasia has been recorded in most metazoans (Leroi et al., 2003). Although, a few exceptional species, such as the naked mole-rat (Heterocephalus glaber) and sharks have been claimed to be resistant to cancer (Finkelstein, 2005; Tian et al., 2013). Recent studies have, however, shown that even these species may develop cancer (Delaney et al., 2016; Finkelstein, 2005) strongly suggesting that the vast majority of multicellular organisms are indeed susceptible to cancer. The frequent occurrence of cancer in metazoans suggests that neoplasia, similar to pathogens/parasites, may have a significant negative impact on host fitness in the wild (Vittecoq et al., 2013). This is supported by a recent review of wildlife cancer by McAloose and Newton (2009) demonstrating that high prevalence of cancer in, for example, Tasmanian devils (Sarcophilus harrisii) and belugas (Delphinapterus leucas) resulted in concomitant significant increase in levels of mortality and reduction in fitness.