The drugsA keener understanding of the biology of cancer cells is leading to the development of less crude forms of treatment which target specific mechanisms within cancer cells rather than killing the cells outright.
Conventional chemotherapy drugs and radiation therapy hit the cell nucleus or engine of the cell so that it can't survive but new drug treatments are now attacking the blood supply of the cells or slowing down their growth, therefore disabling them in a less aggressive manner. For example, a biopsy of a breast cancer tumour can now reveal if there is a deficiency in the mechanism that controls the growth of the cancer. And, in cancers where there is an oversupply of what are known as growth factor receptors, specific drugs can now target this activity only, thus disabling the entire functioning of the cancer cells.
"Twenty per cent of breast cancers have these Her-2 growth factor receptors present in vastly increased amounts and an artificially generated antibody [for example, the drug Herceptin\] has been developed to bind with this protein to destroy it," explains Dr John Kennedy, consultant medical oncologist at St James's Hospital, Dublin. "In some cases, the tumour will shrink without chemotherapy or radiotherapy or in others it will make the \ chemotherapy treatment work better. Studies have shown dramatic results from this treatment with patients responding more quickly, staying in remission longer and living longer."
However, while drugs such as Herceptin don't have the side effects of traditional chemotherapy drugs, some can cause heart problems as the Her-2 receptor has been found to be important in heart function.
Leukaemia is another form of cancer for which new knowledge of the biology of the cancer has led to new drug therapy. A molecular abnormality in a protein known as BCR-ABL was discovered in a form of leukaemia known as chronic myeloid leukaemia. This abnormality makes the cancer cells resistant to standard chemotherapy. A new drug has been developed to target this abnormality.
"This drug has transformed the treatment of chronic myeloid leukaemia. There has been a good response in an enormous number of patients, some of whom have been cured of their cancer," says Dr Kennedy. Based on findings from more sophisticated biological analysis of tumours during diagnosis, they herald in more precision-based treatment approaches that may - for some cancers at least - replace the more toxic, conventional treatments of today.
