What is personalized medicine?
There is no standard medical definition for personalized medicine, so you may hear this term used in different ways. In general, it describes tailoring (or adapting) the treatment of a disease (such as breast cancer) to give the most effective treatment for each person’s disease. To do this, personalized medicine uses information that can include:
- A person's genes
- Non-genetic personal characteristics (for example, lifestyle factors)
- Molecular (cell) characteristics of the disease
Personalized medicine may also be called “precision medicine.”
The importance of personalized treatment
The goal of personalized medicine is to give the most effective treatment for each person’s breast cancer. This involves:
Getting the best results, while avoiding unnecessary treatment. All treatments for breast cancer (including surgery, radiation therapy, chemotherapy, hormone therapy and targeted therapy) have risks and side effects. Avoiding unnecessary treatments avoids these risks and side effects.
- Developing therapies to target specific tumors or specific cellular pathways that lead to tumor growth and identifying the people who will respond best to them.
Some factors that help personalize treatment plans are related to an individual. For example, some treatments are chosen based on whether a woman is premenopausal or postmenopausal.
Most factors that help personalize treatment however, are related to the breast cancer itself. Breast cancers differ in many ways, especially at the molecular (cell) level. These factors related to the tumor give information on prognosis and help personalize treatment to give the most benefit to each person.
How is treatment personalized?
Although treatment is becoming more personalized, we cannot predict how any one person will respond to a certain treatment. Treatment is personalized based upon the groups a person belongs to (such as people with HER2/neu-positive (HER2-positive breast cancers) rather than to a specific person.
The results of clinical trials show us which therapies are most effective in which groups of people. If a certain therapy is effective in a group you belong to, then your treatment plan can be personalized to include that therapy. For example, clinical trials have shown the targeted therapy trastuzumab (Herceptin) lowers the risk of recurrence of HER2-positive breast cancers. If your tumor is HER2-positive, then your treatment plan is usually personalized to include trastuzumab.
Learn more about factors that affect treatment and prognosis.
Factors related to tumors
Information related to your breast cancer diagnosis helps personalize your treatment plan. When breast cancer is diagnosed, a pathologist studies some of the tumor tissue under a microscope and runs some tests on the tissue. The pathologist’s findings describe your final diagnosis and features of the tumor such as size, type and grade. Beyond these basic tumor features, many factors related to the tumor help plan your treatment. For example:
All tumors are tested for certain characteristics that guide treatment. These include:
Sometimes the genetic profile of a tumor can help guide treatment.
- Oncotype Dx® is a tool that looks at a set of 21 genes in tumor tissue to help estimate the potential benefit of chemotherapy in people with estrogen receptor-positive breast cancers. Some tumors are tested with Oncotype Dx.
Learn more about tumor size, tumor type, tumor grade and other pathology findings.
Learn more about hormone receptor status, HER2/neu receptor status and other factors that affect prognosis and treatment.
Learn more about Oncotype Dx and other tumor profiling tools.
Emerging areas - factors related to tumors
Many new targeted therapy drugs are under study for breast cancer treatment. As with most new drugs, these therapies are first studied in the treatment of metastatic breast cancer. Findings from these studies determine whether new drugs become part of standard care for metastatic breast cancer and go on to be studied for the treatment of early breast cancer. Some new targeted therapy drugs are already part of standard care for metastatic breast cancer (learn more). Researchers continue to study ways to personalize therapies to best treat each person and each breast cancer.
Targeted drug therapies
Targeted therapy drugs can be designed to attack certain cancer cells or certain cellular pathways. However, there are many challenges with targeted drug therapy research. For example, some drugs target certain cellular pathways involved in both cancer cell functions and normal cell functions. So, while these drugs may block cancer cell functions and cancer growth, they may also harm healthy cell functions and cause unintended side effects. Researchers must find ways to have such drugs affect only cancer cells and leave healthy cells unharmed.
Some promising targeted drug therapies for metastatic breast cancer include:
- Tyrosine-kinase inhibitors block tyrosine kinase enzymes, which are important in certain cancer cell functions. Lapatinib (Tykerb) is the only one currently FDA-approved for the treatment of breast cancer. (Learn more about lapatinib in the treatment of HER2-positive metastatic breast cancer.) Other tyrosine-kinase inhibitors are under study and are only available in a clinical trial.
- Poly(ADP-ribose) polymerase (PARP) inhibitors block the PARP enzyme, which is involved in DNA repair. Some chemotherapy drugs damage DNA. Adding a PARP inhibitor to these chemotherapy plans may lower the chances the cancer cells become resistant to the chemotherapy. Early findings suggest PARP inhibitors hold the most promise for metastatic breast cancer in people who have a BRCA1 or BRCA2 gene mutation . PARP inhibitors are still under study and are only available in a clinical trial.
Another challenge of targeted therapy research is identifying the people who will get the most benefit from the drug. We may understand how a drug works (and which cancer cell functions it targets), but still need to learn whom the drug can help. For example, the drug bevacizumab (Avastin) blocks angiogenesis (the growth of new blood vessels). Without a blood supply, cancer cannot grow. While studies show bevacizumab does not offer a treatment benefit for all people with metastatic breast cancer, researchers are still studying whether it may offer benefit to people with certain types of metastatic breast cancer. Learn more about bevacizumab.
Learn more about targeted therapies.
Learn more about emerging areas in targeted drug therapies for metastatic breast cancer.
Molecular subtypes of breast cancer
Molecular differences in breast tumors may help guide treatment and the development of new targeted therapies. Most studies divide breast cancers into four molecular subtypes: luminal A, luminal B, triple negative/basal-like and HER2 type. Although mainly used in research setting, these subtypes may be useful in personalizing treatment and developing new therapies in the future.
Learn more about molecular subtypes of breast cancer.
Tumor profiling tests (using gene expression profiling tools) give information about the genes in cancer cells and may help us learn more about differences in breast cancers. Oncotype Dx® is the only tumor profiling tool widely used in the U.S. At this time, other tools are mostly limited to the research setting. Researchers are working to address the technical limits of these tools.
Learn more about tumor profiling.
Learn more about Oncotype Dx.
Genes and personal factors
Although still under study, your genes and personal characteristics (such as lifestyle factors) may also help guide your breast cancer treatment.
At this time, personal genetic information is not used to make treatment decisions. However, certain personal factors help choose treatments. For example, for a woman whose treatment plan includes hormone therapy, whether or not she is postmenopausal guides her drug choices. A woman who is postmenopausal can take tamoxifen or an aromatase inhibitor, while a woman who is premenopausal can only take tamoxifen.
Personal preferences also play a role in some treatment decisions.
Emerging areas - genes and personal factors
As we increase our understanding of how a person’s genes affect breast cancer, we can use that knowledge to personalize treatments. Being able to identify genes that might predict a person’s response to a specific therapy would help inform and personalize treatment decisions. For example, PARP inhibitors may offer more benefit for metastatic breast cancers in women who have a BRCA1 or BRCA2 gene mutation compared to cancers in women without these mutations (learn more).
Lifestyle factors and other personal characteristics may also help us to personalize treatments in the future. These topics are under active study.
Treatment of breast cancer continues to improve through findings from clinical trials. Clinical trials test the benefits of new treatments, diagnostic and screening methods and risk-lowering strategies. People volunteer to take part in these research studies. Whether a new therapy or test becomes part of standard breast cancer care depends largely on clinical trial results. If you have breast cancer, we encourage you to consider joining a clinical trial.
Susan G. Komen® in collaboration with BreastCancerTrials.org offers a custom matching service that can help you find a clinical trial that fits your health needs.
Learn more about clinical trials.
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date at this time.