Chemotherapy describes the use of a chemicals to inhibit or kill an unwanted cell or organism. In medicine, the concept is applicable to the treatment of infectious diseases caused by bacteria, viruses, parasites, and neoplastic growth (cancers). The essential activity of all types of chemotherapy depends upon the interference with normal biochemical processes in the target cell with resulting disruption in cell function leading either to death or to the inability to produce viable progeny.
Drug-induced cell injury is dependent upon a number of factors, including the extent of drug entry into the cell, the nature of the metabolic or structural lesion produced, the cells' capacity to circumvent the lesion by an alternate pathway, replacement or repair, and the length of time permitted for repair before the lesion becomes lethal (i.e., before the cell attempts to undergo replication). If the drug inflicts damage and lingers (is not cleared), the repair process may not be able to keep up with the rate of damage, in which case if the cell tries to divide, it may die or else produce non-viable or non-proliferatve progeny.