If you or a loved one has been diagnosed with metastatic breast cancer (MBC), you’re likely wondering what the treatment journey will look like. With so many treatment options available, it’s easy to become overwhelmed. Chemotherapy is one of the most common cancer treatments, and it typically plays a large part in managing MBC. In fact, nearly everyone with MBC will receive chemotherapy at some point.

In this article, we’ll discuss what chemotherapy is and why it’s used to treat MBC. We’ll also cover common chemotherapy drugs and drug combinations used for MBC management. If you have specific questions about chemotherapy for your breast cancer, talk to your oncologist (cancer specialist).

Chemotherapy Is a Key Treatment for Metastatic Breast Cancer

The word “metastatic” refers to cancer that has metastasized (spread) from the primary tumor to other parts of the body. Between 6 percent and 10 percent of people diagnosed with MBC have de novo cancer. This means that breast cancer has metastasized before it was diagnosed. As a result, local treatments, those used to treat a specific area — like surgery and radiation therapy — likely won’t be effective.

Instead, oncologists will typically recommend bodywide or systemic therapies for treating MBC. Chemotherapy is used to kill cancer cells. Your oncologist may prescribe a chemotherapy drug that’s taken orally (by mouth) or injected intravenously (IV infusion, into a vein).

Nearly all people with MBC will be treated with chemotherapy at some point. Some receive this treatment soon after their diagnosis, while others take it after other medications haven’t been successful. The timing of chemotherapy treatment depends on details about the genetic mutations (changes) found in your cancer cells after a biopsy. Neither chemotherapy nor other treatments currently available are likely to cure MBC. However, chemo may be used as a palliative treatment to improve your MBC symptoms. This type of treatment focuses on relieving symptoms and improving quality of life rather than curing the disease.

Hormone Receptor-Positive MBC and Chemotherapy

Not everyone with MBC starts treatment with chemotherapy right away after diagnosis. Some people may receive other treatments like hormonal therapy, which stops the hormones that help cancer cells grow, or targeted therapy, which targets specific molecules involved in cancer growth.

These medications target hormone receptors (HRs) and other proteins on the surface of breast cancer cells. Your doctor will first start by testing your cancer cells to see if they contain:

• Estrogen receptor (ER)
• Progesterone receptor (PR)
• Human epidermal growth factor receptor 2 (HER2)

The types of HRs and proteins your cancer cells have will influence your breast cancer treatment plan. People with ER-positive and HER2-negative MBC usually receive hormonal therapy first. Examples include tamoxifen or an aromatase inhibitor, such as anastrozole or letrozole. An aromatase inhibitor is a type of medication used mainly in the treatment of breast cancer. It works by blocking the enzyme aromatase, which the body uses to make estrogen. Estrogen can make some breast cancers grow faster.

If your cancer stops responding to hormonal therapy, the next step is chemotherapy. Oncologists typically use just one chemotherapy drug rather than a combination. This is different from early-stage breast cancer treatment, when oncologists usually prescribe multiple chemotherapy drugs at the same time.

If you have HR-positive, HER-negative MBC that progresses after hormonal therapy and chemotherapy, your doctor may recommend a targeted treatment like abemaciclib (Verzenio).

HER2-Positive MBC and Chemotherapy

People with HER2-positive MBC are usually treated with chemotherapy and medications that block HER2. Examples of HER2 therapies include pertuzumab (Perjeta) and trastuzumab (Herceptin). If your cancer stops responding to these drugs, you have other options. Examples include:

• Antibody-drug conjugates (ADCs) — Protein drugs that deliver chemotherapy directly to cancer cells
• Kinase inhibitors — Drugs that block proteins that send growth signals in cancer cells
• Other protein drugs that block HER2

Fam-trastuzumab deruxtecan-nxki (Enhertu) is an antibody-drug conjugate used to treat HER2-positive MBC. This is a protein (antibody) drug that delivers toxic chemotherapy directly to cancer cells. Kinase inhibitors can be given in combination with chemotherapy, HER2 treatment, or both.

Metastatic Triple-Negative Breast Cancer and Chemotherapy

According to the American Cancer Society, 10 percent to 15 percent of breast cancer cases don’t have ER, PR, or HER2. This type of breast cancer is known as triple-negative breast cancer (TNBC). Unfortunately, TNBC can’t be treated with hormonal or targeted therapies. In this case, chemotherapy is recommended as the first treatment. Your oncologist may recommend one or more chemotherapy drugs for metastatic TNBC, depending on details about how your cancer is growing.

Chemotherapy can also be combined with other treatments for TNBC. Around 20 percent of people with TNBC have PD-L1 on the surface of their cancer cells. Oncologists can use immunotherapy to block PD-L1 and treat TNBC. For example, your oncologist may prescribe pembrolizumab (Keytruda) with chemotherapy.

If your MBC progresses after trying two other treatments, you can try an ADC. Sacituzumab govitecan (Trodelvy) is an ADC that delivers chemotherapy directly to your cancer cells.

Chemotherapy Drugs for Treating Metastatic Breast Cancer

Doctors and researchers have developed several chemotherapies for breast cancer. Your oncologist will work with you to decide which treatment option will be your best option. They’ll take your overall health, personal preferences, and the drug’s potential side effects into consideration. Examples of chemotherapy for MBC include:

• Taxanes — Docetaxel (Taxotere)
• Platinum-based chemotherapy — Cisplatin and carboplatin (Paraplatin)
• Anthracyclines — Doxorubicin and epirubicin (Ellence)
• Antimetabolites — Capecitabine (Xeloda) and fluorouracil (5-FU)

The specific type of breast cancer you have plays a role in the type of chemotherapy you get. For example, HER2-positive MBC is typically treated with a taxane. People with metastatic TNBC may receive several kinds of chemotherapy. People whose cancer cells have BRCA1/BRCA2 mutations are often treated with platinum-based chemotherapy.

Chemotherapy Schedules for Metastatic Breast Cancer

Chemotherapy is given on a regular schedule based on findings from clinical trials. You may need treatment once a week, once every other week, or even just once a month. You’ll receive a certain number of treatments per cycle, and then you’ll likely take a break. The exact schedule will depend on the specific chemotherapy drug you’re given.

Here are a few examples of how chemotherapy schedules work. Capecitabine comes as a pill that’s taken twice daily for 14 days, followed by seven days of rest. Doxorubicin is given as an IV infusion over the course of one hour. You’ll need to visit a hospital or infusion center for your treatment. You can receive a higher dose of doxorubicin once every three weeks or a lower dose once weekly for three weeks. Afterward, you’ll have a week of rest.

If you have questions about your chemotherapy treatment schedule, your oncologist or a member of your cancer care team can help.

Chemotherapy Treatment Comes With Side Effects

MBC is an advanced stage of cancer. Your oncologist will want to limit your side effects to improve your quality of life. Chemotherapies are effective in killing cancer cells. However, they also destroy your healthy cells. This is why most people with MBC will be treated with only one chemotherapy drug at a time.

Possible side effects of chemotherapy include:

• Nausea and vomiting
• Hair loss
• Mouth sores
• Fatigue
• Back pain from nerve damage
• Easy bruising and bleeding
• Loss of appetite and weight loss
• Increased risk of infections

Your oncologist can explain what other side effects you may experience. Your side effects depend on the type of chemotherapy you receive.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 68,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you been treated with chemotherapy for metastatic breast cancer? Do you have advice for anyone who’s starting their treatment journey with MBC? Share your experiences in the comments below, or start a conversation by posting on your Activities page.