Tumor Biology and Natural History

Tumors are not uniform diseases but heterogeneous entities consisting of cell populations called cell clones, with different genetic and molecular features. The ability of a tumor to evolve and fit to host microenvironment, by developing often resistance mechanisms to the anticancer therapies, is dependent on this biological variability. In fact, the variability observed within individual tumors, known as intra-tumor heterogeneity, represents the crucial step in cancer clonal evolution process, by promoting and driving a genetic mechanism able to select the fittest cell clones. A single clonal origin is usually shown by most of tumors at the early stages of the disease, whereas advanced-stage tumors may contain multiple cell populations with different characteristics.