Research into the causes, prevention, and treatment of breast cancer is under way in many medical centers throughout the world.
Causes of breast cancer
Studies continue to uncover lifestyle factors and habits that alter breast cancer risk. Ongoing studies are looking at the effect of exercise, weight gain or loss, and diet on breast cancer risk.
Studies on the best use of genetic testing for BRCA1 and BRCA2 mutations continue at a rapid pace. Scientists are also exploring how common gene variations may affect breast cancer risk. Each gene variant has only a modest effect in risk (10 to 20%), but when taken together they may potentially have a large impact.
Potential causes of breast cancer in the environment have also received more attention in recent years. While much of the science on this topic is still in its earliest stages, this is an area of active research.
A large, long-term study funded by the National Institute of Environmental Health Sciences (NIEHS) is now being done to help find the causes of breast cancer. Known as the Sister Study, it has enrolled 50,000 women who have sisters with breast cancer. This study will follow these women for at least 10 years and collect information about genes, lifestyle, and environmental factors that may cause breast cancer. An offshoot of the Sister Study, the Two Sister Study, is designed to look at possible causes of early onset breast cancer. To find out more about these studies, call 1-877-4-SISTER (1-877-474-7837) or visit the Sister Study Web site (
www.sisterstudy.org).
Chemoprevention
Results of several studies suggest that selective estrogen-receptor modulators (SERMs) like tamoxifen and raloxifene may lower breast cancer risk in women with certain breast cancer risk factors. But so far, many women are reluctant to take these medicines because they are concerned about possible side effects.
Newer studies are looking at whether aromatase inhibitors -- drugs such as anastrozole, letrozole, and exemestane -- can reduce the risk of developing breast cancer in post-menopausal women. These drugs are already being used as adjuvant hormone therapy to help prevent breast cancer recurrences, but none of them is approved for reducing breast cancer risk at this time.
Fenretinide, a retinoid, is also being studied as a way to reduce the risk of breast cancer (retinoids are drugs related to vitamin A). In a small study, this drug reduced breast cancer risk as much as tamoxifen. Other drugs are also being studied to reduce the risk of breast cancer.
New laboratory tests
Gene expression studies
One of the dilemmas with early-stage breast cancer is that doctors cannot always accurately predict which women have a higher risk of cancer coming back after treatment. That is why almost every woman, except for those with small tumors, receives some sort of adjuvant treatment after surgery. To try to better pick out who will need adjuvant therapy, researchers have looked at many aspects of breast cancers.
In recent years, scientists have been able to link certain patterns of genes with more aggressive cancers -- those that tend to come back and spread to distant sites. Some lab tests based on these findings, such as the Oncotype DX and MammaPrint tests, are already available, although doctors are still trying to determine the best way to use them.
Classifying breast cancer
Research on patterns of gene expression has also suggested some newer ways of classifying breast cancers. The current types of breast cancer are based largely on how tumors look under a microscope. A newer classification, based on molecular features, may be better able to predict prognosis and response to several types of breast cancer treatment. The new research suggests there are 4 basic types of breast cancers:
Luminal A and luminal B types: The luminal types are estrogen receptor (ER)–positive, usually low grade, and tend to grow fairly slowly. The gene expression patterns of these cancers are similar to normal cells that line the breast ducts and glands (the lining of a duct or gland is called its lumen). Luminal A cancers have the best prognosis. Luminal B cancers generally grow somewhat faster than the luminal A cancers and their outlook is not quite as good.
HER2 type: These cancers have extra copies of the HER2 gene and several other genes. They usually have a high-grade appearance under the microscope. These cancers tend to grow more quickly and have a worse prognosis, although they often can be treated successfully with targeted therapies such as trastuzumab (Herceptin) and lapatinib (Tykerb).
Basal type: Most of these cancers are of the so-called triple-negative type, that is, they lack estrogen or progesterone receptors and have normal amounts of HER2. The gene expression patterns of these cancers are similar to cells in the deeper basal layers of breast ducts and glands. This type is more common among women with BRCA1 gene mutations. For reasons that are not well understood, this cancer is also more common among younger and African-American women.
These are high-grade cancers that tend to grow quickly and have a poor outlook. Hormone therapy and anti-HER2 therapies like trastuzumab and lapatinib are not effective against these cancers, although chemotherapy can be helpful. A great deal of research is being done to find better ways to treat these cancers.
It is hoped that these new breast cancer classifications might someday allow doctors to better tailor breast cancer treatments, but more research is needed in this area before this is possible.
Tests of HER2 status
Determining a breast cancer's HER2 status is important to get an idea of how aggressive the cancer might be and to find out if certain drugs that target HER2 can be used to treat the disease.