Treatment for breast cancer is becoming more and more personalized. There is ongoing research to better tailor therapies to best treat each person’s breast cancer. Factors related to the tumor itself (such as hormone receptor status) can guide treatment. And, factors related to each person (such as genes) may also help in choosing which treatments will work best.
For information on promising, new treatments for metastatic breast cancer, visit the Emerging Areas in Metastatic Breast Cancer section.
Gene Expression Profiling
Gene expression profiling is a promising area in breast cancer treatment. This technology uses the genetic profiles of cancer tumors to predict which cancers may be more aggressive and, therefore, more likely to benefit from chemotherapy [20]. These tests do not show a genetic profile of your personal traits, but rather a profile of the tumor. Those whose tumor gene profiles show a high risk of recurrence may be more likely to choose chemotherapy, as they stand to benefit from it more than those whose profiles show a low risk of recurrence. People at low risk may choose to avoid chemotherapy altogether, choosing instead hormone therapy (for hormone receptor-positive cancer) or observation alone. At this time, the gene profiling test OncotypeDx can be used to help make chemotherapy treatment decisions in people with lymph node-negative, estrogen receptor-positive cancers [21]. Other genetic profiles and their use in guiding treatment plans are still under study [22].
Subtypes of breast cancer
There is a growing interest in understanding the molecular and genetic differences in breast cancers to guide the development of new targeted therapies. One current theory divides breast cancers into four molecular/genetic subtypes: luminal A, luminal B, basal-like and HER2/neu-positive. Although these subtypes are not yet used in clinical settings, in the future, they may be useful in the development of targeted treatments. Currently, subtyping is done only in the context of a research study. For more information on subtypes of breast cancer, visit the Diagnosis section.
CYP2D6 and Tamoxifen
There is early evidence that information about some genetic factors may prove helpful when choosing treatment for a person. One possible factor is the gene CYP2D6, which appears to affect how the body metabolizes (breaks down and uses) tamoxifen. Some people have a genetic variation (a certain form of the gene) that results in little or no CYP2D6 function. Others have a variation leading to higher than normal CYP2D6 function. Some small studies have looked at the CYP2D6 gene in postmenopausal women with breast cancer being treated with tamoxifen. These studies found that women with gene variations related to less CYP2D6 function had a higher risk of recurrence than women with genes related to normal or high CYP2D6 function [23-25].
Although some insurance companies now cover genetic testing for CYP2D6, it is not a part of standard care at this time. While having high levels of CYP2D6 enzyme may show that a person has a better chance of responding to tamoxifen, having less of the enzyme does not mean that tamoxifen will not be effective. Also, the best way to test for the CYP2D6 variation is still not known since many different types of genetic variations may be involved. Because of these issues, genetic testing for CYP2D6 is not widely used.
Certain medicines can interfere with CYP2D6 enzyme function and should be avoided while taking tamoxifen [23]. For example, some antidepressants, such as fluoxetine (Prozac) and paroxetine (Paxil), can interact with CYP2D6 and may affect how tamoxifen works in the body [23]. Women are who are considering taking tamoxifen should talk with their health care provider about potential drug interactions. For more on tamoxifen, visit the Hormone Therapy section.
Updated 08/26/09
