Clone wars: the evolution of therapeutic resistance in cancer

Cancer chemotherapy kills some tumour cells, leaving behind resistant clones with less competition for space and resources. These clones, groups of cells that share common ancestry, proliferate without restriction causing disease relapse. Tumours contain a host of cancer clones that are genetically and epigenetically different from one another [1]. These clones follow a Darwinian process of somatic selection where they compete for space and resources within their microenvironments [2]. Cancer cells acquire mutations over time that affect their fitness, giving some clones a survival advantage over others [3]. Chemotherapy itself is a selective pressure that influences tumour heterogeneity and clonal evolution. Most cancer deaths are caused by clones that are therapeutically resistant [3]. The evolution of resistant clones occurs rapidly, resulting in the appearance of new clones that are not susceptible to conventional therapy. Evolutionary principles describe the process of clonal evolution and aid in formulating novel strategies for disease management and prognosis [4].