Individual therapy: New dawn or false dawn?

The sequencing of the human genome brings with it the hope that greater understanding of genetic components of disease will allow the more specific targeting of therapies. It has also been suggested that it will permit sponsors to run "cleaner" clinical trials with less variability and a consequent saving in patient numbers., However we do not know how much of the variation in response that we see from patient to patient in clinical trials is genetic, because we rarely design the sort of trials that would allow us to identify patient-by-treatment interaction. Such interaction provides an upper bound for gene-by-treatment interaction for a group of patients studied since patients differ by more than their genes. On the other hand, however the variability seen within a clinical trial may generally be expected to be less than the total variation that would be seen within a population. There is a related statistical issue to do with the interpretation of effects from clinical trials. This arises because there is confusion between experimental and sampling models of clinical research. It is concluded that we may have to pay careful attention to certain design features of clinical trials if we wish to make progress in this field.