Not long ago, cancer patients worldwide were offered the same few treatment options — chemotherapy, radiation, or surgery — regardless of the type of cancer or stage.
Enter precision treatments, a method that allows doctors to customize treatment specific to your needs.
Whether you were recently diagnosed with breast cancer or have already begun treatment and are questioning your treatment plan, there are many options you and your doctor can choose from.
What Are Precision Treatments?
Instead of relying primarily on more aggressive approaches such as chemotherapy, which also kills healthy cells, the goal of a precision approach is to target the cancer and nothing else.
George Sledge, MD, former chief of oncology at Stanford Medicine and past president of the American Society of Clinical Oncology, says much of precision medicine comes down to what you can learn about each patient.
"The more we know about your tumor, the better we can treat it. It's that simple," says Sledge, who's now executive vice president and chief medical officer at Caris Life Sciences.
How Tests Are Used to Tailor Treatment Plans
Thanks to medical advancements, there are tests that can help doctors determine how likely you are to get breast cancer. They can even predict the odds of it coming back.
"Early detection is really key in breast cancer survival," says Cassie Hajek, MD, medical director at Helix, a genomics company. "The earlier you can detect it, the better chance we have of getting rid of it and preventing recurrence."
Other tests can tell doctors what treatments may work for you and which ones probably won't, which means no unnecessary side effects.
"Now, we know who's going to benefit," Sledge says. "And we only use the drugs in that setting."
Here's a look at the tests.
Biomarker testing
Biomarker tests look for substances — in tissue, blood, or other bodily fluids — that point to disease. The samples are first tested for cancer cells. Any cancer cells found are then tested for three different receptors, which helps determine the subtype:
- An estrogen receptor (ER)
- A progesterone receptor (PR)
- A human epidermal growth factor receptor 2 (HER2)
There are two main tests used to find HER2 and hormone receptors in breast cancer:
Immunohistochemistry (ICH) test. This measures how much HER2 is on a cell. Depending on the results, the cancer is classified as either HER2-positive or HER2-negative. It can also show if tumor tissue or cancer cells have estrogen and progesterone receptors. The cancer will be either hormone receptor-positive (HR-positive) or hormone receptor-negative (HR-negative).
Fluorescence in situ hybridization (FISH) test. If ICH results are unclear, this test can look at the gene responsible for encoding HER2 to see if there are a higher than normal amount of copies, which means the cancer is HER2-positive.
Genomic testing
Genomic testing finds genetic mutations, or changes, in tumor cells. Doctors can then recommend therapies to target them. For example, about 30%-40% of patients with HR-positive/HER2-negative breast cancers have a PIK3CA mutation. Your doctor might recommend a PI3K inhibitor if they find this mutation in your sample.
Genomic tests can also help predict how well chemotherapy will work. The Oncotype DX Breast Recurrence Score test is one example of this. It analyzes 21 genes to anticipate the risk of recurrence.
Genetic testing
Genetic tests look for certain gene mutations in a patient's DNA that can raise their risk of cancer. For example, if a BRCA1 mutation is found but the patient has not been diagnosed with breast cancer, they now have the opportunity to think about preventive treatment.
Precision Treatment Options
Here's an overview of the types of precision treatments available.
Hormone therapy
Hormone therapy lowers your body's hormone levels or stops hormones from latching on to cancer cells.
Selective estrogen receptor modulators (SERMs) are one type. They keep estrogen (which fuels cell growth) from attaching to breast cancer cells.
Aromatase inhibitors are another option. They block the enzyme that makes estrogen. They're often prescribed to postmenopausal women and those assigned female at birth. Those who are premenopausal may be prescribed medication that blocks the activity of estrogen. More serious cases may need surgical removal of the ovaries to stop estrogen production completely.
The most reported side effects of hormone therapy are:
- Hot flashes
- Night sweats
- Vaginal dryness
If you're premenopausal, this kind of therapy can disrupt your menstrual cycle.
Targeted therapy
Targeted therapies zero in on proteins that control how cancer cells grow, divide, and spread. Most are small-molecule drugs, medications small enough to enter cells. Or they're monoclonal antibodies, lab-made immune system proteins designed to target cancer cells in a specific way.
Potential side effects of targeted therapy include:
- Allergic reactions
- Hair loss
- Heart damage
- A weakened immune system
Immunotherapy
Immunotherapy gives your immune system a leg up in the fight to find and kill cancer cells. Cancer cells are sneaky and have ways of getting around your body's built-in protection. They may:
- Have gene mutations, or changes, that make them harder for your immune system to recognize
- Have proteins on the surface that turn off your immune cells
- Change the healthy cells around the tumor, which affects how your immune system responds to the cancer cells
The types of immunotherapy used to treat breast cancer include:
- Immune checkpoint inhibitors
- Monoclonal antibodies
Potential side effects of immunotherapy include:
- Infusion reactions, such as a rash and swelling
- Diarrhea
- Fatigue
- Cough
Antibody-drug conjugates
Antibody-drug conjugates (ADCs) deliver chemotherapy straight to cancer cells. An ADC contains an antibody, or protein, that recognizes a specific marker on the cancer cell. The antibody is combined with both a cytotoxic drug that kills cancer cells and a linker protein that holds the antibody and cytotoxic drug together. The antibody attaches itself to the cancer cell, and it puts the chemotherapy right inside of it.
ADCs are usually prescribed after other treatments stop working, but some are approved for earlier use. One of these is fam-trastuzumab deruxtecan-nxki (Enhertu). It was first approved by the FDA in 2019 for treatment of HER2-positive metastatic breast cancer that did not respond to two previous treatments. It was approved in August 2022 for HER2-low breast cancer in those with cancer that had spread (metastatic) or couldn't be removed with surgery (unresectable) and who had tried chemotherapy.
In January 2025, it received broader approval for HR-positive, HER2-low, or HER2-ultralow metastatic breast cancer that has progressed after at least one round of endocrine therapy. HER2-low or HER2-ultralow means there is a level of HER2 on the cancer cells but not enough HER2 to be considered HER2-positive.
Datopotamab deruxtecan (Datroway) was also approved in January 2025 to treat HR-positive, HER2-negative breast cancer in those who did not respond to hormone therapy and chemotherapy.
Potential side effects of ADCs include:
- Hematological toxicity
- Nausea
- Diarrhea
- Ocular disorders
- Peripheral neuropathy, which damages the nerves outside the brain and spinal cord
How Precision Treatments Are Used Alongside Other Therapies
Precision treatments are often combined with other treatments such as chemotherapy and surgery. They can also be used before or after other treatment methods.
Before primary treatment
Sometimes, secondary treatments are given before more aggressive treatments such as chemotherapy or surgery. This is called neoadjuvant therapy.
Neoadjuvant therapy can help make the primary treatment more successful. For example, a surgeon may want to use chemotherapy to shrink a tumor before operating, to make surgery easier.
After primary treatment
Secondary treatments can also be given after the primary or more aggressive treatment. This is called adjuvant therapy. Adjuvant therapy is sometimes used to kill cancer cells left over after the primary treatment. It can also be used to lower the chances of the cancer coming back.
Factors That Affect Treatment
Along with the subtype, other factors play a role in what treatment your doctor recommends. These include:
- How quickly a tumor is growing
- Genetic mutations
- Overall health, age, and menopausal status
- Prior treatments
What to Ask Your Doctor
Consider asking your doctor these questions when discussing your treatment plan:
- What treatment do you recommend and why?
- What is the standard treatment for this type of cancer?
- How many people have you treated with this plan? What were the results?
- What other treatments are appropriate for my type of cancer?
- What are the pros and cons of the treatment you're recommending?
- Can you refer me to someone for a second opinion?
- What percentage of patients typically respond to this treatment?
- How long does each treatment appointment last? How long is the entire course of treatment?
- How often will I be treated?
- Will there be tests during my treatment to figure out if it's working?
- What will the treatments feel like?
- Can someone come with me to treatment?
- Can I drive to and from my appointments?
- Can I be alone after treatment or will someone have to stay with me?
- Will I have to be in the hospital to receive treatment?
- Who will give my treatments?
- How often will I see my doctor or nurse during treatment?
- Are there foods or medications or activities that I should avoid during treatment?
- How soon after treatment can I go back to work?
