The Enigma of Cancer Polyploidy as Deciphered by Evolutionary Cancer Cell Biology (ECCB)

Evolutionary Cancer Cell Biology (ECCB) reveals that the majority of cancer hallmarks trace their origins back to the premetazoic era, approximately 2300 to 1750 million years ago. These cancer hallmarks share deep homology with the oxygen-sensitive non-gametogenic NG (Urgermline), which evolved from the common ancestor of Amoebozoan, Metazoan, and Fungi (AMF). The genes, gene modules, and gene regulatory networks of the premetazoic cell system are preserved in the ancestral genome compartment of metazoans and humans. The Urgermline serves as a blueprint for all germ and stem cell lineages, including parasitic amoebae. As observed in amoebae, DNA double-strand breaks (DSBs) manifest in the homologous recombination (HR) genes of NG germlines and stem cell lineages when exposed to specific hyperoxic conditions, referred to as AMF hyperoxia, characterized by an oxygen content exceeding 6.0%. The cells lose their stemness and differentiation potential but persist in proliferation as low-grade polyploids (4n) through defective symmetric cell division (DSCD phenotype). Genomic integrity can be restored through homotypic cell and nuclear fusion, resulting in the formation of high-grade polyploids known as multinuclear genome repair syncytia (MGRSs), or by inductive hyperpolyploidization of more than 64n, as observed in single-celled polyploid giant cancer cells (PGCCs). Interestingly, low-, middle-, and high-grade polyploidization are not exclusive to cancer. Therefore, we investigate (i) functional polyploidies that occur in healthy cells, including humans, mammals, and protists, (ii) dysfunctional polyploidies that occur in cells with impaired homologous recombination (HR) and irreparable DNA DSB defects, and (iii) the restoration of genome integrity through cyst-like and high-grade polyploidization events. Additionally, we explore dysfunction in aging stem cells, hepatocytes, and cardiomyocytes