Features of clonal proliferation and adaptive evolution in neoplastic cells: Similarities between cancer cells and clonal organisms

The clonal proliferation of neoplastic cells within a body and the clonal propagation of living organisms in a habitat are essential components of neoplastic and clonal population growth, respectively. In a favorable habitat, the number of clonal organisms increases exponentially up to the carrying capacity or to a niche size that reflects a specified sensitivity for environmental factors. This phenomenon corresponds to benign neoplasms in a body. For malignant neoplasms, neoplastic cells invade the surrounding tissue and metastasize to distant organs via the evolution of subclones that expand their niche size or carrying capacity by changing their genomes. This is an evolutionary mechanism that characterizes neoplastic cells in an organism, but has not yet been discovered for organisms other than bacteria. In humans, cancer cells treat medical treatments and the immune system as environmental disturbances within the organism. By accumulating genetic changes such as mutations, a neoplasm produces multiple subclones with differing genomic constitution. Such cell evolution can be represented as a phylogenetic tree. The spatial distribution of cancer cells in a tissue is a patchy structure of clones because of the genetic heterogeneity of neoplastic cells, environmental heterogeneity of the habitat tissues, and limited dispersal ability of subclones. In conclusion, a comparison of the concept of clonality between the cell and organism levels would give new insights into research in both cancer biology and ecology.