Final answer:
About 20-25% of breast cancers exhibit characteristics such as being HER2-positive, estrogen receptor-negative, or triple-negative, which influences their treatment options.
Step-by-step explanation:
The characteristics of 20-25% of breast cancers are varied, but some key features include being HER2-positive, which means there's an overexpression of the HER2 protein due to gene duplication. Drugs like Herceptin (trastuzumab) have been developed to target this overexpression, helping to remove HER2 and control its signaling, thus aiding in the treatment of breast cancers. Some breast cancers are estrogen receptor-negative, which implies that they do not have receptors for estrogen; these cancers would not respond to therapies that target estrogen receptors. Additionally, some breast cancers are classified as triple-negative, which means they lack estrogen receptors, progesterone receptors, and excess HER2 protein. This type of breast cancer can be particularly challenging to treat because it does not respond to hormonal therapy or medicines that target HER2.