Cytogenetic abnormalities in cancer: with special emphasis on tumor heterogeneity.

There is a considerable amount of cytogenetic data available to support the statements that (1) cancer is a genetic disease; (2) most cancers are monoclonal in origin; (3) tumor cells are more genetically unstable than normal cells; (4) the genetic instability may be inherited, acquired, or both during the lifespan of the individual tumor; (5) tumor metastasis is a nonrandom, controlled process, and clonal in origin; (6) malignant tumors are genetically heterogeneous and contain multiple subpopulations that may differ in their biological properties; (7) some tumors might be difficult to treat successfully because of their resistant nature; and (8) tumor cells may acquire resistance because of gene amplification. For these reasons it is extremely important to study the biology of malignant tumor cells in order to determine their effective treatments and control this dreadful disease.