Definition

Abnormal growths of tissue composed of cells that have lost normal growth control, characterized by uncontrolled proliferation.

Synthesis

Tumors are established as complex, heterogeneous ecosystems characterized by uncontrolled cell proliferation driven by accumulated genetic alterations, including driver mutations, copy number changes, and chromosomal instability. A key mechanistic relationship emerges between chromosomal instability and immune surveillance: chromosomally unstable tumors generate immunogenic heterogeneity that attracts increased immune cell infiltration, representing a fitness cost that aneuploid cancer cells must overcome through specific immune evasion strategies, particularly the inactivation of Stat1 signaling often coupled with increased Myc activity. This evolutionary adaptation is conserved between mouse and human aneuploid cancers, suggesting a fundamental solution to the challenge of immune recognition. Within individual tumors, single-cell analyses reveal extensive intratumoral heterogeneity manifesting across spatial and temporal dimensions, with cells exhibiting continuous spectra of stemness states, variable responses to hypoxic conditions, and diverse transcriptional programs related to oncogenic signaling. What remains contested is whether the molecular signatures derived from bulk tumor profiling accurately capture tumor biology, as single-cell resolution exposes these population-level measurements as potentially artifactual averages that obscure the true cellular diversity and subclonal dynamics driving therapy response and tumor evolution.