It’s not enough just to understand breast cancer; it’s important to understand your breast cancer.
In the past, we saw breast cancer as one disease, but now we know better. Breast cancer is a general term used to refer to cancer that occurs in the breast, but there are actually several different types of breast cancer, each driven by its own set of underlying biological factors.
Because each breast cancer is unique, breast cancer treatment must also be unique—and there has been a distinct shift to fighting cancer at the molecular level. In fact, there is even a name for it: personalized medicine.
Personalized medicine is the result of ongoing research into the genetics, genomics and molecular biology of cancer. As we deepen our understanding of the underlying biology and behavior of cancer, we develop more personalized and targeted ways to treat it.
Your cancer is unique
Historically, breast cancer was simply “staged” (how big is it and where is it in the body?). Of course, staging is still important, but now in addition to staging, we can identify molecular subtypes of the cancer. This additional information helps guide treatment, enabling doctors to provide personalized medicine.
In order to identify the individual “fingerprint” of a breast cancer, doctors will look at many characteristics of the cancer:
Stage is a measure of the extent of the cancer, and is based on the size of the tumor and the presence or absence of local or distant metastases (cancer spread). There are several important variables in staging breast cancer:
Invasive vs. non-invasive:
Noninvasive breast cancer, also called “in situ,” refers to cancer in which the cells have remained within their place of origin and have not spread to breast tissue around the breast duct or lobule. There are two types of noninvasive cancer:
- Ductal carcinoma in situ (DCIS) is considered precancerous and could develop into invasive cancer if not removed.
- Lobular carcinoma in situ (LCIS) is not considered precancerous.
Invasive breast cancer refers to cancer that has spread outside the membrane that lines a duct or lobule, invading the surrounding tissues. Breast cancer that has reached stages I to IV is considered invasive.
The size of a cancer helps determine its stage. Smaller cancers are considered earlier stage cancers and are often more treatable. For example, a stage I cancer is smaller than 2 centimeters and has not spread outside the breast, whereas a stage III cancer may be 5 centimeters with spread to the lymph nodes.
Lymph node involvement
Determining whether cancer has spread to the lymph nodes is an important part of staging. When lymph nodes contain cancer cells, there is an increased risk of the cancer spreading. The more lymph nodes that contain cancer cells, the more serious the cancer might be.
Aggressiveness is determined based on how cancer cells look under the microscope. It is measured by the degree of difference between cancer cells and normal cells and graded on a scale of 1 to 3, with grade 3 cancers being the most aggressive.
Approximately 20 percent of breast cancers overexpress (make too much of) a protein known as HER2. Overexpression of this protein leads to increased growth of cancer cells. It is important to accurately measure HER2 status in all breast cancers because there are targeted treatments for HER2-positive cancers.
Hormone receptor status
Some breast cancer cells express an abundance of receptors for the female hormones estrogen and/or progesterone. These hormone receptor-positive breast cancers are typically associated with a better prognosis and are treated differently from breast cancers that are hormone receptor-negative. Patients with hormone receptor-positive breast cancer often receive treatment with hormonal therapy (such as tamoxifen or an aromatase inhibitor).
Breast cancers can be classified as estrogen receptor (ER)-positive, progesterone receptor (PR)-positive, or hormone receptor-negative.
Among women with early-stage breast cancer, the expression, or activity, of certain genes has been linked with the likelihood of cancer recurrence.
There are three genomic tests available to measure gene expression and predict the likelihood of recurrence: Oncotype DX, MammaPrint, and Mammostrat. Based on the results of these tests, women are assigned a Recurrence Score (for Oncotype DX) or a risk index score that predicts the risk of recurrence. Women at a higher risk of recurrence may benefit from more aggressive treatment, whereas those with a lower risk may be spared additional treatment.
The right treatment at the right time
Understanding all of the characteristics of a woman’s breast cancer—including the genomics—enables doctors to customize treatment to target the specific characteristics of the cancer.
No longer is a woman simply diagnosed with breast cancer. Now, the cancer is identified as either estrogen receptor (ER)-positive or ER-negative and HER2-positive or HER2-negative. This additional information is fundamental to guiding treatment.
Women with HER2-positive cancer will benefit from treatment with the targeted drug Herceptin® (trastuzumab), whereas those with HER2-negative cancer will not. Similarly, women with ER-positive cancer may benefit from hormonal therapies designed to suppress or block estrogen, whereas those with ER-negative cancer will not.
What’s more, there are three genomic assays — Oncotype DX, MammaPrint, and Mammostrat — that are designed to examine the genetic structure of a woman’s breast cancer and predict its behavior. These tests may help guide decisions about whether additional treatment with chemotherapy or radiation therapy is necessary after surgery. Individuals with high-risk cancers may require more aggressive treatment, while those with low-risk cancers may be spared from unnecessary treatment.
The importance of clinical trials
Clinical trials are studies that evaluate the effectiveness and safety of new drugs or treatment strategies.
What do clinical trials have to do with breast cancer treatment? A lot, actually. Most new treatments are developed in clinical trials. All new cancer drugs that are currently available in the United States were once only available in clinical trials.
Clinical trials are essential to advancing new and innovative treatment strategies. In fact, personalized treatment strategies—such as Herceptin or hormonal therapy—are now available to breast cancer patients as a direct result of the clinical trials process.
In order to develop more effective breast cancer treatments, it is important that patients continue to participate in clinical trials. Participation in a clinical trial may offer access to better treatments and advance the existing knowledge about treatment of this cancer.
Clinical trials are available for most stages of cancer. Patients who participate in a clinical trial can expect to receive the best current standard treatments available or new treatment strategies that may one day become standard treatment. In some cases, the best cancer treatment may be available only in a clinical trial.
- National Human Genome Research Institute. Frequently Asked Questions About Genetic and Genomic Science. Available at: http://www.genome.gov/19016904 (Accessed April 16, 2014).
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- Solin LJ, Gray R, Baehner FL, et al. A multigene expression assay to predict local recurrence risk for ductal carcinoma in situ of the breast. Journal of the National Cancer Institute. 2013; 105(10): 701-710.
- Smith, I, Proctor M, Gelber RD et al. 2-year Follow-up of Trastuzumab after Adjuvant Chemotherapy in HER2-positive Breast Cancer: A Randomised Controlled Trial. Lancet. 2007;369:29-36.
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