Triple-negative breast cancer (TNBC) is a subtype of breast cancer characterized by the absence of three specific receptors that are commonly found in other types of breast cancer. The three receptors are:

1. Estrogen receptor (ER): Hormones such as estrogen can promote the growth of some breast cancers. In TNBC, the cancer cells do not have receptors for estrogen.

2. Progesterone receptor (PR): Similar to estrogen, progesterone can also stimulate the growth of certain breast cancers. TNBC lacks receptors for progesterone.

3. Human epidermal growth factor receptor 2 (HER2): HER2 is a protein that can promote the growth of cancer cells. TNBC is negative for HER2 amplification or overexpression.

The absence of these three receptors makes triple-negative breast cancer distinct from other types of breast cancer, such as hormone receptor-positive or HER2-positive breast cancers. Triple-negative breast cancer tends to be more aggressive and may have a poorer prognosis compared to other subtypes. Treatment options for TNBC are often limited because it does not respond to hormone therapies or drugs targeting HER2 receptors. Chemotherapy is a common approach for treating triple-negative breast cancer, and ongoing research is focused on finding more effective targeted therapies for this subtype. It's important for individuals diagnosed with TNBC to work closely with their healthcare team to determine the most appropriate treatment plan for their specific case.