[Chromosomes and drug resistance of tumors]

Since most cancers eventually become refractory to chemotherapy, the development of drug resistance within tumour populations remains a major concern in the cancer treatment. The development of drug resistance is often correlated with specific chromosomal modifications. Though chromosomal aberrations are generally much more frequent in cancer than in normal cells, there are no qualitative differences between the aberrations in cancer and in normal cells. At present the genetic basis of drug resistance may be induced by gene amplification, which can be alternatively associated with chromosomal homogeneously stained regions or with double microchromosomes. The both phenomena are essentially the same: they reflect the mechanism for the amplification of genes stimulating tumour viability under unfavourable conditions.