Abstract: Breast cancer is caused by somatic mutation.As such, somatic mutation in breast cancer should be described to elucidate the underlying mechanism.Next-generation sequencing has provided new insights into the genomics of breast cancer.New genes were identified and exhibited a relationship with breast cancer.Although these genes mutated at a low frequency, such genes in different cases could be categorized into specific pathways.Mutational signatures could be found in some cases, but such signatures were generally not related to environmental exposure.Studies on intra-tumoral heterogeneity have revealed the ubiquitous presence of sub-clones in breast cancer; however, a major clone is also observed, accounting for >50% of tumor cells.Current advancements show that breast cancer genomics has been integrated into personalized medicine.Furthermore, a genome-informed and personalized molecular sub-typing and treatment of breast cancer can be developed in the future.