Clinical Implications of Tumor-Cell Heterogeneity

THE genetic changes that are important for the expression, maintenance, and progression of the malignant phenotype are responsible for the extensive diversity of cells observed in the neoplastic process. This phenomenon, termed tumor-cell heterogeneity, is a fundamental property of cancer that has important biologic and clinical consequences.1 , 2 Morphologic heterogeneity that is characterized by nearly normal differentiation and marked anaplasia is often observed within a single neoplasm. The biochemical properties of neoplastic cells within the same tumor may also vary. An important and frequent example occurs in breast cancer, in which malignant cells that are positive for cytosolic estrogen or progesterone . . .