1 For individuals
In some instances a particular intervention is eective only in subgroups of individuals with a particular disorder. Targeting therapy in such a way is not new. Appropriate antimicrobial therapy has, for many years, been based wherever possible on the nature of the infectious agent and its sensitivity pattern. Advances in genomic medicine and molecular biology, however, are leading to redenitions of disease and a more personalized approach to therapeutics.3 Trastuzumab, for instance, is eective only in women with breast cancer whose tumour cells express the human epidermal growth factor 2 (Her2) receptor.4 Similarly, the eects of cetuximab on overall survival in individuals with advanced colorectal cancer are dependent on the presence of the wildtype Kras epidermal growth factor receptor rather than the mutated form:5 the hazard ratio for overall survival was 0.55 (95% condence interval (CI) 0.41 to 0.74) in tumours expressing the wild-type Kras, compared with 0.98 (95% CI 0.70 to 1.37) in tumours expressing the mutated form.