Most patients respond to chemotherapy in the short term, but, particularly in the case of bladder cancer, patients who respond over the long term to a given drug are rare, and the cancer often recurs. Lee hopes that the model will help match patients with drugs that will work over the long term.

The gene chips used for the studies, made by Affymetrix, now cost only $260. Theodorescu says that this price is "trivial compared to imaging," such as the magnetic resonance imaging and PET scans routinely used in clinical trials. And he says that the price could come down if researchers used Affymetrix chips customized for particular cancer types.

Most hospital laboratories don't have the resources to perform and interpret gene-expression analysis. But Theodorescu hopes it will become a routine part of patient care in the next five or ten years, complementing the under-the-microscope tissue analysis currently used to characterize cancers.