A classification of breast cancers is based on the receptors it expresses. Three main receptors are studied: ER or estrogen receptor; RP or progesterone receptor; and HER2.
Triple negative breast cancer is cancer in which the hormone receptors, estrogen and progesterone receptors, and HER2 are negative.
Consequently, this type of cancer is more resistant to pharmacological treatment as it does not respond to hormone therapy (such as tamoxifen or aromatase inhibitors) or to therapies aimed at HER2 receptors, such as Herceptin (generic name: trastuzumab), with other treatments such as surgery (lumpectomy or mastectomy), radiotherapy and other chemotherapies other than Herceptin taking on special importance.
About 10-20% of breast cancer cases are triple negative, and due to their resistance to treatment they are also more aggressive.