Research into the mutations of a gene known as EGFR that can be found altered in lung cancer may help to determine the response of a new group of pharmaceutical – the tyrosine quinase inhibitors of the epidermic growth factor receptor. Also, the presence of genetic changes in specific fragments of PDGFR-alfa genes as well a sin the c-kit gene can pinpoint which treatment is likely to be more efficacious in certain gastrointestinal sarcomas. In this respect, the Department of Oncology at the University Hospital (University of Navarra) and the Centre for Applied Medical Research (CIMA) of the same University are collaborating in the identification of these genetic changes based on the study of the tumour prior to the application of treatment in the patient. We are currently analysing genetic changes which will help us define the parameters needed to interpret what the best set of pharmaceutical drugs might be to act on certain tumours, particularly cancers of the lung, of the colon and sarcomas. DIn this way, which patients best respond to a specific treatment can be identified. At the same time, we manage to know the toxicity profile that may occur using these medicinal drugs. The procedure consists of a genetic analysis of a blood sample or of the cancerous tissue where the existence of certain mutations or polymorphisms are observed and enable us to predict what drugs are the most suitable for that particular patient. The analysis provides us with information about the most effective therapeutic option against the tumour, as well as what the potential side-effects are of this treatment on the patient. In this way a better therapeutic selection and individualisation for each patient is achieved. The analysis of certain genetic variants called polymorphisms help to predict an increased toxicity risk due to treatment with certain antineoplasic pharmaceuticals. Providing the most suitable drug to each patient will mean reducing the symptoms of the toxicity - fatigue, digestive indisposition, cutaneous reaction, diarrhoea, vomiting, as well as alterations in the liver and kidney. In this way the patient will have a better quality of life. A number of research projects undertaken by different teams have confirmed the use of these markers for response and toxicity and their role in drawing up more individualised therapeutic plan.