Breast Cancer: Estrogen+

As I am sure most of you that are familiar or have done any reading on breast cancer have heard the term ER+ (positive), or Estrogen positive. But what exactly does being ER (estrogen) positive really mean, what are the implications and significance to breast cancer patients of being tested for Estrogen positive or negative? What role does estrogen play in breast cancer? Today I would like to take the time and explain what Estrogen+ (positive) is, what it means, and the role it has in breast cancer.

What does Estrogen+ (positive) mean?

Inside of a woman’s body is a hormone called estrogen. Estrogen is a lot like testosterone, it is the predominat female sex hormone in women, much like testosterone is in men. Estrogen levels are at their highest levels in women typically during puberty. They help to promote the growth of the secondary sex characteristics such as breasts, are involved in thickening of the endometrium, as well as other aspects of the menstrual cycle in women. When it comes to breast cancer, the reference to Estrogen positive (denoted as ER+ in the rest of this posting) means that the cancer cells have ear like projections or antennae on the surface of the cell.


For example, if you can picture that the projections in the above diagram are like antennae sending out signals for estrogen, and then the ligands are the estrogen coming in to connect with one another. This would be a good example of how estrogen receptors work, and how estrogen ends up connecting with them on the cells surface.

Once the Estrogen connects to the cells receptor, it then begins to send signals to the inside of the cell, and instructing it to grow. As we have learned in my previous post on What Is Cancer? we know that the formal rules for cell growth have been turned off. Since the rules for growth have been turned off, and there are now more receptors then normal on the surface of the cell asking for the body to send more Estrogen, once that Estrogen arrives at the cell receptor, then connects, it sends additional signals inside of the cell telling the cancer to grow and divide into more breast cancer cells.

In this above diagram, you can see the normal progression of how a cancer cells forms, and when you add an ER+ receptor to the mix, it allows for additional uncontrollable cancer growth.

What percentage of Breast Cancer is ER+?

  • About 75% of all Breast Cancers are ER+ (estrogen receptor positive.)
  • About 65% of all ER+ Breast Cancers are also positive for another female hormone called progesterone.
  • About 25% of Breast Cancers are negative, or ER/PR-, or an unknown status.
  • About 10% of Breast Cancer is ER+ and PR-
  • About 5% of Breast Cancer is ER- and PR+
  • If cells have receptors for one OR both Estrogen and/or Progesterone, the cancer is then said to be hormone receptor positive.

In te above context, positive means that the cells have been tested and that a “significant” amount of cells have receptors on them. Negative means that the cells do not have an abnormal amount of receptors on them.

Unfortunately each hospital and lab have different criteria for testing and defining what number of receptors need to be present in the cancer cell in order to be called positive or negative. As a rule of thumb, if there is at least 5-10% of cells that have receptors present, it will then be defined as Positive. This is why it is very IMPORTANT to note what percentage of receptors were found on the cells. If your report comes back as negative, but there is still a 5% indication of cells that tested positive, there may still be a likelihood that you might respond well to Hormonal Therapy.

If your report comes back negative, there are typically three reasons for this:

  1. The test was never ordered or performed.
  2. The smaple of tissue that the laboratory received was too small in order to test appropriately for the state of receptors being present or not.
  3. Few estrogen and/or progesterone receptors were present.

How to test for ER+ Breast Cancer?

After a patient either has a lumpectomy or a mastectomy and the breast cancer tissue is removed, it can then be sent to a lab in order to be tested. Once in the lab, if the tissue is shown to have either estrogen or progesterone receptors present, or both are present, then the patient is said to be positive. This also means that there is a high indication that the patient may also be a good candidate for hormone therapy with a high likelihood to respond to this form of treatment as well. The more Estrogen or Progesterone present on the cell, the higher the likelihood that hormonal therapy will work. If both are present in high numbers, the chances for success with hormonal therapy is even greater. Another name for hormonal therapy is, Anti-Estrogen Therapy.

How does Hormone Therapy work?

Estrogen and Progesterone travel through the body via the bloodstream. As they travel through the body, they will search for those little antennae that are sitting outside or inside the surface of the cell. Once they find the matching receptor that it fits inside of, it will then connect to one another and turn on the mechanism for the cancer cell to grow. It is much like a key fitting into a lock. Once the key fits and the door is unlocked, you are freely able to get inside and turn the cells ability to grow uncontrollably to the “On” position.

So what happens with Hormone Therapy, or also called Tamoxifen, the Tamoxifen will travel through the bloodstream and will seek out the ER receptors on the surfaces of the cancer cells. Once they have sought them out, they will then fit into the locks of the  receptors and take up the space. By doing so, it prevents Estrogen from coming along and fitting into that same lock and turning the growth switch for the cancer cell to on. It keeps it in the off position.


As you can see in the above diagram, hormone therapy, or the use of tamoxifen in ER+ patients, inhibits the cancers ability to recruit more Estrogen into the cell, thus eliminating the ability to turn on the growth mechanism for the tumor. As more receptors are present on or in the cell, the more Tamoxifen can connect to the receptor and inhibit the ability of Estrogen to promote growth of the cancer cell. This will end up leading the cancer cells to withering and dying since there is no instructions for them to continue their growth.

Tomorrow I will talk more about what it Tamoxifen and Reloxifene and their roles in women with breast cancer as hormone therapies.

As always, if you or a loved one have any other questions, comments, or concerns; if you would like more information in regards to another cancer related topic, please contact me at: CANCERGEEK@GMAIL.COM or CANCERGEEK@CANCERGEEK.COM



4 responses to “Breast Cancer: Estrogen+

  1. Pingback: Cancer Resource Directory » Blog Archive » Colorectal Cancer - Tour de Cure: Cancer stats

  2. Cancergeek-

    Thank you for your comment. I’m definitely enthusiastic about our school’s Relay for Life event this year and I hope to participate in other ACS activities as well.

    Are you from the Boston area? We look for motivational speakers to come talk to the participants in order to inform, educate.

    Would you be interested?


  3. Cancergeek-

    Thank you for your comment. I’m definitely enthusiastic about our school’s Relay for Life event this year and I hope to participate in other ACS activities as well.

    Are you from the Boston area? We look for motivational speakers to come talk to the participants in order to inform, educate.

    Would you be interested?

    P.S. What you’re doing on this site is awesome. Hope is everything.

  4. Thank you for your information, it has helped to understand what these terms mean. I have had many unanswered questions that by reading this website, I have been able to have a clearer picture.

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