The invention relates to a method to predict the response to treatment with radiotherapy combined with cisplatin-based chemotherapy in patients with cancer, preferably non-microcytic lung cancer, wherein said method is based on the detection of the presence of methylation in the IGFBP-3 gene. The present invention also relates to an in vitro method to design a customised treatment for an individual with said disease. The method of the invention may be quantitative or semi-quantitative. The present invention also relates to a probe designed for the quantitative detection of the methylation of the IGFBP-3 gene, to a kit that comprises it and to the use of the kit to predict the response of a subject to the aforementioned treatment.