What’s New in Decoding Breast Cancer

It has become apparent that breast cancer is a very complex disease that can affect individuals with seemingly identical clinicopathologic parameters very differ- ently. For this reason, molecular classification of breast cancer is becoming increasingly important in determining treatment strategies for individual patients. By using gene expression profiling on a genome-wide level for breast cancer, one can distinguish different molecular subtypes that have a similar biological behaviour. These subtypes are designated as luminal A, luminal B, basal and ERRB2. Even though these subtypes were developed without consideration of patient outcome, there are striking differences in aggressiveness between subtypes. Prognosis for patients with luminal A subtype is significantly better than for patients that have the basallike and ERBB2 subtypes, for which the survival times are shorter. The substratification of the luminal group into A and B subgroups has important prognostic implications; however, for determining the need for chemotherapy, more accepted characteristics for therapeutic decision-making – including risk stratification by multigene assays (gene expression signatures) – are preferred.