The diagnosis of breast cancer often leads patients into a state of fear of the unknown.

Often, the experiences of family members or friends tend to make patients think their experience with breast cancer will be the same or similar. There are many factors that determine how invasive breast cancer behaves and how, we as providers, treat this disease.

We now know that the most important driver in breast cancer behavior and treatment is what I call the “biology of the tumor.”

Specifically, the hormone receptor status of the tumor. The three receptors we look at are Estrogen (ER), Progesterone (PR) and Human Epidermal Growth Factor (HER2).

A patient can have many combinations of these receptors, and this is the driving force of breast cancer behavior and treatments.

Treatment is targeted to these receptors and can greatly impact tumor growth and lower risk for recurrence.

Most breast cancers are ER positive. These are usually slower growers and carry a better prognosis.

Triple Negative breast cancers, (ER-, PR-, HER 2-) are more aggressive and tend to grow faster. With Triple Negative breast cancers, none of the receptors are present.

Likewise, HER2 positive tumors are also more aggressive and tend to grow faster. Treatment modalities that are targeted to these receptors can greatly impact tumor growth and lower risk for recurrence.

Hormone positive tumors, (ER+, PR+) can be treated with hormone blocking pills such as Tamoxifen. HER 2+ tumors can be treated with immunotherapy that targets these receptors such as Herceptin or Perjeta. These drugs can lead to remission in about 60% of these more aggressive tumor types.

Most Triple Negative breast cancers, (ER-,PR-,HER2-) will require and benefit from chemotherapy. The most favorable biology are the “Luminal A” cancers that are ER+, PR+, HER2 -. Not all of these will require chemotherapy. The same is true for “Luminal B” cancers that are ER+, PR-, HER2 -.

I hope that this brief, simplified breakdown will give patients an idea of what their specific biology means for them. Certainly, there are more details that will be discussed with patients based on their tumor biology and cell type. The take home message is this: every breast cancer is different, and your specific treatment will be directed at your specific tumor biology.

Every breast cancer is different, and your specific treatment will be directed at your specific tumor biology.