Stem cells emerged in evolution at the point of transition to stable multicellularity. This increase in hierarchical complexity requires robust mechanisms to maintain tissue homeostasis and organism integrity, and to stably interact with the environment. tumorDysfunction of stem cell activity is expected to lead to cancer formation. Computational analysis of genes involved in cancer formation revealed their early emergence in metazoan evolution and predicted that all metazoans might be prone to develop tumors (Domazet-Lošo & Tautz, 2010).
Recently we provided the first evidence for naturally occurring bona fide cancer in two species of Hydra (Domazet-Lošo, Klimovich et al., 2014). Histological, cellular and molecular data reveal that tumor cells originate by differentiation arrest of female-restricted germ-line progenitors. The tumor cells have migration capacity, are able to induce de novo tumor formation, and show a greatly altered transcriptome that mimics expression shifts in vertebrate cancers. Our study revisits the essential role of differentiation arrest and resistance to apoptosis in driving cancerogenesis. In sum, our findings suggest that evolutionary origin of spontaneous cancers dates back to the origin of Metazoa, and imply that the ability for tumor formation goes side by side with such evolutionary innovations as multicellularity and stem cells.