What is estrogen receptor positive breast cancer?

Estrogen-SensitiveCA: Normal breast cells have estrogen receptors which are like locks that estrogen "keys" fit into. Many breast cancer cells also have these estrogen receptors, which is good for 2 reasons: (1)these cancers tend to be less aggressive (since they resemble normal breast cells), and; (2)"anti-estrogens" such as tamoxifen can be very effective chemotherapeutic agents for these cancers.

One with receptors.: These are tumors with estrogen receptors on them. This makes them susceptable to some chemotherapeutic agents, like tamoxifen.