Molecular profiling of breast cancer: portraits but not physiognomy

Breast cancers differ in response to treatment and may have a divergent cli nical course despite having a similar histopathological appearance. New tec hnology using DNA microarrays provides a systematic method to identify key markers for prognosis and treatment response by profiling thousands of gene s expressed in a single cancer. Microarray profiling of 38 invasive breast cancers now confirms striking molecular differences between ductal carcinom a specimens and suggests a new classification for oestrogen-receptor negati ve breast cancer. Future approaches will need to include methods for high-t hroughput clinical validation and the ability to analyze microscopic sample s.