Women diagnosed in any stage of breast cancer will soon be able to get a more comprehensive test that will help doctors plan their treatment. Developed by Charles Perou and colleagues, the test predicts the aggressiveness of breast tumors and anticipates how cancer will respond to chemotherapy.

The test uses fifty genes to classify a tumor as one of four subtypes that vary in prognosis and drug susceptibility, and require different courses of treatment. For example, the test can identify estrogen-receptive tumors, helping some patients who might traditionally have been given chemotherapy avoid it in favor of hormone-blocking drugs. Other tumors of the aggressive Luminal B subtype don’t respond well to chemotherapy or to hormone-blocking drugs, making them good targets for cutting-edge therapies.

Although the new test looks for a complex set of traits, it uses technology that’s already in many pathology clinics. “Instead of sticking with the microarray platform that we used to discover the genes, we chose a platform called quantitative RT-PCR,” Perou says. “Some labs may already have much of the equipment needed to run the assay.”

A study of about seven hundred patients published in February 2009 confirmed the test’s ability to predict how tumors will respond to chemotherapy. Larger clinical trials are under way. The patent-pending test is being marketed by University Genomics and ARUP Laboratories as the Breast Bioclassifer, and will be available commercially in summer 2009.