Key biological events and determinants of resistance to cancer therapy include the ability of tumor cells to survive therapeutic insults, tumor heterogeneity, physical barriers to therapeutics due to intermingled stromal tissues, inflammatory and immune reactions in the tumor microenvironment, the presence of mutations in driver genes (e.g., K-ras) with no known inhibitors, and the consequences of therapeutic pressures [208]. This evidence concerns the gene KRAS and neoplasm.