Frozen tumor samples from 140 node-negative, breast cancer patients aged between 29 and 70 years at diagnosis are hybridized on MammaPrint array. Patients were treated with breast conserving therapy or mastectomy with axillary lymph node dissection between December 1998 and August 2001 at Osaka Medical Center for Cancer and Cardiovascular Diseases. Samples are evaluated by gene expression profiling for the 70-gene MammaPrint profile and classified as genomic high risk or genomic low risk.