Overview of the complex interactions among molecular classifications of TNBC based on genomic, transcriptomic, proteomic, epigenomic, and immune characterization of the tumor and its microenvironment. Overview of the complex interactions among molecular classifications of TNBC based on genomic, transcriptomic, proteomic, epigenomic, and immune characterization of the tumor and its microenvironment. ER, estrogen receptor; PR, progesterone receptor; Mut, mutant; RTK, receptor tyrosine kinase; MMR, mismatch repair; CNA, copy-number alteration; AR, androgen receptor; HRD, homologous recombination deficiency; IHC, immunohistochemistry. Ana C. Garrido-Castro et al. Cancer Discov 2019;9:176-198 ©2019 by American Association for Cancer Research