Biomarkers for therapeutic efficacy
Depending on the tumour type, a larger or smaller number of cancer patients receive chemotherapy with systemic toxicity as the only effect. In that situation, an alternative, not necessarily medical, treatment would have been a better choice - and toxicity (and financial resources) could have been spared by withholding ineffective drugs. One of the reasons for this apparent paradigm is that the tumour cells of each cancer pa- tient may show different sensitivity/resistance towards different chemotherapeutic drugs, i.e. breast cancer or colorectal cancer is not only breast or colorectal cancer. With our increasing biological insight and understanding, it has become apparent that each patient's tumour tissue is unique and as a consequence, each patient's tumour cell sensitivity/resistance to- wards chemotherapeutic drugs may be different. As of today there is no method in routine clinical use to predict the sensitivity/resistance to chemotherapy in its broad sense in the individual patient. This chapter will describe several different DNA, RNA, protein and cell based assay methodologies and marker molecules that have been brought forward as potential predictive assays/markers to be used to select the most effective drugs for the individual cancer patient.