Tumor heterogeneity refers to the genetic and phenotypic variation observed between tumors of different tissue and cell types, which arises due to differences in genetic backgrounds, pathological patterns, differentiation stages, mutation spectra, and gene expression profiles between tumor cells. This heterogeneity is an important feature of malignant tumors, contributing to diversity in their genetic makeup, structures, developmental stages, mutations, and molecular characteristics. Understanding and accounting for tumor heterogeneity is important for cancer research and developing effective treatment strategies.