An average risk woman in the US has about a 1 in 8 chance of developing breast cancer. Breast tumors are genetically heterogeneous and can be classified into subtypes based on patterns of gene expression, DNA methylation, nucleotide substitutions and genomic rearrangements. Dr. Åke Borg is Professor of Oncology and Pathology at Lund University, and he joined me to discuss the genetics of breast cancer.