Triple-negative breast cancer (sometimes abbreviated TNBC) refers to any breast cancer that does not express the genes for estrogen receptor (ER), progesterone receptor (PR) and HER2/neu. This makes it more difficult to treat since most hormone therapies target one of the three receptors, so triple-negative cancers often require combination therapies. Triple negative is sometimes used as a surrogate term for basal-like; however, more detailed classification may provide better guidance for treatment and better estimates for prognosis.Triple-negative breast cancers comprise a very heterogeneous group of cancers. There is conflicting information over prognosis for the various subtypes, but it appears that the Nottingham prognostic index is valid and hence general prognosis is rather similar with other breast cancer of same stage, except that more aggressive treatment is required. Some types of triple-negative breast cancer are known to be more aggressive, with poor prognosis, while other types have very similar or better prognosis than hormone receptor positive breast cancers. Pooled data of all triple-negative subtypes suggest that, with optimal treatment, 20-year survival rates are very close to those of hormone positive cancer.Triple-negative breast cancers have a relapse pattern that is very different from hormone-positive breast cancers: the risk of relapse is much higher for the first 3–5 years, but drops sharply and substantially below that of hormone-positive breast cancers afterwards. This relapse pattern has been recognized for all types of triple-negative cancers for which sufficient data exist, although the absolute relapse and survival rates differ across subtypes.