Systemic therapies (chemotherapy)
Systemic means that a –drug (in the case of cancer, a chemotherapeutic agent) is introduced into the bloodstream. This allows it to act on the entire organism. A chemotherapeutic agent must therefore be able to distinguish between healthy cells and cancer cells, in the same way as an antibiotic must be able to differentiate between the normal cells of the body and harmful bacteria.
Rapid cell division often constitutes an identifying feature which is characteristic of cancer cells. There are, however, also healthy cells which undergo frequent cell division, for example, in the hair glands, gastrointestinal mucous membrane and the system for manufacturing blood cells. Although a course of chemotherapy may destroy up to 99.9% of the cancer cells, it is almost inevitable that these healthy cells will suffer from severe side effects. Moreover, cancer cells may very quickly become resistant to the chemotherapeutic agent by mutating, or, in other words, undergoing a change in genetic material.
The domains of systemic therapy are diffuse tumours, such as blood cancer (leukaemia). They also include other metastases that cannot be diagnosed and localized on account of their microscopic size. Chemotherapy is also a suitable treatment method in the case of solid tumours which cannot be treated surgically or through radiation.