Molecular mechanisms involved in DNA repair, in gene rearrangement and in gene amplification may be considered as an integrated system in maintaining cellular homeostasis and cell survival.

In procaryotic and also in eucaryotic cells, several systems for repairing the DNA damage have been discovered. The mechanism and genetic control of DNA excision-repair and SOS have been extensively studied. These repair processes help prevent lesions from interfering with DNA functions or from converting into permanent mutations that cause cellular malfunctioning and cell death, which in higher organisms contribute to malignancy. However, other molecular systems can be identified which contribute to the maintenance of homeostasis and the survival of the cell. The system that maintains the DNA superstructure is one of these while gene amplification allows the cell to become resistant to a particular environmental change and survive in the presence of chemical compounds like drugs. Our purpose was to group in a major system the molecular systems which, until now, have always been considered as separate entities. The common basis of all these systems is the capacity to maintain genetic information or to permit the survival of the cell. The system, called the "Cell Survival Molecular System" (CSMS), is composed of several well known molecular systems, such as DNA repair, which are able to restore the DNA structure and genetic mechanisms. Moreover, the Cell Survival Molecular System may also give a selective advantage to the cell so that it can grow in a hazardous environment. Following on from this, the relationship between CSMS and cancer will be discussed. The development and the progression of the cancer may be the result of the growth of an "adapted cell". This may adapt to, or resist, a new or changed environment. In addition, genetic defects can occur in CSMS and these will probably give an impaired function to some systems in CSMS. These defects could be associated with inherited or familiar cancer.