What happens when a tumor continues to grow despite treatment? Insensitive to chemotherapy, cancer cells through many different processes can be or. Some of them are based on detoxification mechanisms. Other tumors do not respond to cytotoxic drugs, because they went the ability to natural cell death, apoptosis, is lost. What are the mechanisms of the so-called resistance are known so far and why chemosensitivity testing currently in practice make little sense to show the Cancer Information Service at the following text.
Detoxification - not desirable in cancer
Resistance to chemotherapy, albeit to a lesser extent, by the natural detoxification mechanisms of the body arise. If a person into contact with harmful substances to ensure the tissues of the intestine, kidney or liver that toxins are flushed out as soon as possible. Some tumor cells behave like the decontamination specialists in these organs, even if they arise from very different tissue types.
Scientists have discovered genetic changes that lead to activation of such a detoxification function. They are moreover often greatly accelerated.
Such tumor cells to chemotherapy can harm less: With speed, they create the cytotoxic drugs to the outside, regardless of whatever cell poison it is.
This so-called multidrug resistance tends to work on a variety of cytotoxic drugs equally negative. Of about 50 different proteins and the underlying genes, we now know that they can be involved in this type of resistance, the National Cancer Institute of the United States in an English-language press release of August 2004 (www.cancer.gov/newscenter/pressreleases/
ABCtransporterproteins).
Some tumors are much more fundamental changes, which protect them from therapy: The wall of the tumor cells compared with normal tissue, for example, modified so that it transmits no more toxins. Or a larger tumor is so poorly supplied with veins that cytotoxic drugs are no longer transported through the blood into his heart.
This problem of poor accessibility has long been known. Many strategies thus aim to make tumor cells more sensitive to cytostatic drugs and achievable. This happens, for example by combination with radiation therapy (chemoradiation). Researched will be keyed to substances that accumulate in cells better than chemotherapy agents themselves and act as a carrier.
Overcome resistance to cause: The cell death
Resistance may also arise, however, that despite severe damage to a cell does not die away: as a breakthrough in research will see experts in the knowledge that plays in cancer development of a failure of "programmed cell death" a great role (more on that in introductory chapter). The failure of these so-called apoptosis, is probably very often not only responsible for resistance to chemotherapy, but also for the insensitivity to radiation therapy.
As one of the key genes that are responsible for the controlled death of diseased or damaged cells by cytotoxic drugs, is a gene called p53. Shortly after the discovery of its importance, there was, therefore, researchers who called for the cessation of all chemotherapy in patients whose tumors showed a defective p53 gene - because the cells could not die, were cytotoxic meaningless. Today it is known that p53 is only one of several key genes: There are other pathways in which a diseased or damaged cells can occur by cytostatics in the process of programmed cell death.
Background to this "suicide program" in the journal Cell has summarized "insight" of the German Cancer Research Center: www.dkfz.de/de/presse/veroeffentlichungen/einblick/download/2005/einblick-3-2005_web.pdf, Page 36
* The p53 test has found its place in the research, however, belongs - like other chemosensitivity tests also - not for routine diagnosis.
Continue to : Chemosensitivity: Testing before treatment?
Posting Komentar