Up to 30% of patients with early-stage breast cancer will go on to develop a metastatic form of the disease—here's what to know.

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Breast cancer is one of the most common cancers in the world, making up an estimated 11.7% percent of new diagnosed cancer cases globally in 2020, according to data from the American Cancer Society. The National Institutes of Health also estimates that about 13% of women (or those assigned female at birth) in the US will be diagnosed with breast cancer at some point in their lives. The gist: The odds that you or someone you know have, will have, or have had breast cancer are relatively high.

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That's not supposed to be a scary statement. Thanks to incredible advancements in treatment over the course of decades, most people are able to successfully treat their breast cancer and never look back. The exception here is with a diagnosis of metastatic breast cancer—either as an initial diagnosis or a subsequent one following an earlier diagnosis.

Metastatic breast cancer is an incurable form of the disease, but that doesn't mean there are no options for treatment, or that everyone who gets the advanced form of the disease will follow the same timeline. Here's an overview of everything you need to know about metastatic breast cancer, straight from top oncologists.  

What is metastatic breast cancer?

Metastatic breast cancer, also known as stage 4 breast cancer, is the most advanced form of the disease. "Metastatic breast cancer starts in the breast and spreads beyond the breast and lymph nodes to go to other organs," Dean Tsarwhas, MD, medical director of cancer services for Northwestern Medicine Lake Forest Hospital, tells Health. He says breast cancer most commonly spreads to the bones, liver, lungs, and brain, although it can go anywhere in the body.

There are an estimated 155,000 women living with metastatic breast cancer in the US, according to 2017 data published in Cancer Epidemiology, Biomarkers & Prevention. Most of those cases occur in patients who had previously been diagnosed with an earlier stage of breast cancer, Nancy Lin, MD, an oncologist who specializes in breast cancer at Dana-Farber Cancer Institute in Boston, tells Health. In fact, a 2020 review in the British Journal of Cancer shared that 20%-30% of patients diagnosed with an earlier-stage breast cancer still die of a metastatic form of the disease. This can happen either because breast cancer doesn't respond to treatment and spreads, or because it is recurrent, meaning that it returns after going into remission.

Less commonly, patients can be diagnosed with metastatic breast cancer at their initial diagnosis, which means doctors only find the disease when it's already spread to areas outside of the breast. This is known as de novo or primary metastatic breast cancer, and it affects only about 6% of patients with metastatic breast cancer, per the American Cancer Society.

How does breast cancer spread?

For the majority of patients with metastatic breast cancer, it means an initial earlier-stage diagnosis spread to distant parts of the body. According to the National Cancer Institute (NCI), cancer cells spread throughout the body in a series of steps.

The first step of metastasis for any type of cancer—not specifically breast cancer—is when cancer spreads to nearby healthy tissue in the body. The cancer can then continue to spread to nearby lymph nodes or blood vessels in the body, per the NCI. Once cancer cells move into the body's lymph nodes or blood vessels, they essentially gain access to the body's lymphatic system (which moves a fluid called lymph throughout the body) and bloodstream. With that access, cancer cells can stop in a distant location in the body, invade blood vessel walls, and then move into surrounding tissue, growing there until a new tumor forms. New blood vessels then grow to create a blood supply to the new tumor to help it continue to grow.

It's important to note that this doesn't happen with every cancer diagnosis—most cancer cells will die during this process. But, per the NCI, as long as conditions in the body are "favorable," metastasis can happen. Some metastatic cancer cells can also remain at a distant site for years, inactive, before they begin to grow again (or at all).

As Dr. Tsarwhas explained earlier, breast cancer specifically can spread anywhere in the body, but most often spreads to the brain, bone, liver, and lungs.

What are the symptoms of metastatic breast cancer?

The symptoms of metastatic breast cancer vary depending on where the cancer has spread in the body. Evelyn Toyin Taiwo, MD, hematologist and oncologist at Weill Cornell Medicine and NewYork-Presbyterian Brooklyn Methodist Hospital, tells Health these symptoms, based on which part of the body is affected, include: 

  • Bone: New, unexplained pain in bones and joints; commonly seen in the hip or lower back
  • Liver: Abdominal pain or discomfort
  • Lungs: Shortness of breath and cough 
  • Brain: Headaches and dizziness

There are also some full-body symptoms that can occur in metastatic breast cancer patients, says Dr. Taiwo, such as fatigue, unexplained weight loss, and lack of appetite. 

How is metastatic breast cancer diagnosed? 

Currently, there's no one test that can diagnose metastatic breast cancer. How the cancer is diagnosed depends on where it has spread in the body, Alberto Montero, MD, director of the breast cancer program at University Hospitals Seidman Cancer Center in Cleveland, Ohio, tells Health.

In most cases, a diagnosis begins with someone with a history of breast cancer reporting a new, unusual symptom to their doctor, Dr. Montero says. This would prompt tests and imaging (say, an X-ray or CAT scan) that would lead to a diagnosis of metastatic cancer. If a former breast cancer patient says they have worsening leg or knee pain, for example, their doctor might order an X-ray and bone scan to check for cancer lesions in those areas. 

"We really pay attention to people's symptoms," says Dr. Lin. "If somebody with a known prior history of early breast cancer calls with any suggestive symptoms, then we go on to do scans or tests focused on the areas that are having symptoms." This is not to say that everyone with a history of breast cancer who reports headaches or abdominal pain has metastatic cancer. But doctors know to investigate further if they have a breast cancer patient with unusual symptoms, because they could indicate a cancer recurrence. 

This is different from how earlier-stage breast cancer is diagnosed, says Dr. Lin. In those cases, breast cancer is usually detected through a mammogram, and then confirmed with an ultrasound and then a biopsy to confirm the diagnosis. 

Sometimes mammograms fail to detect breast cancer, or sometimes a person is unable to get their regular preventative tests—making a person unaware that they are sick. In those cases, their breast cancer ends up getting diagnosed incidentally. For example, a person might fall and break a bone, says Dr. Taiwo, and then their X-rays will show additional lesions. Further testing will then reveal that the lesions were caused by metastatic breast cancer. 

How is metastatic breast cancer treated?

The drugs and treatments used to treat metastatic breast cancer are typically the same as what's used to treat earlier stages of breast cancer. Think: chemotherapy, radiation, immunotherapy, and targeted hormone therapies. 

As with earlier stages of the disease, metastatic breast cancer treatment also depends on the subtype of cancer, says Dr. Tsarwhas. An estrogen-positive cancer (meaning that the cancer cells have estrogen receptors on them) typically gets some kind of hormonal therapy, while an HER2-positive cancer (aka cancer cells with high amounts of the protein HER2) will often get an antibody treatment targeting the HER2 proteins. Meanwhile, triple-negative breast cancer (a cancer subtype that lacks hormone receptors or high amounts of HER2 proteins) doesn't respond to hormonal therapies or HER2 antibody treatments, so it requires chemotherapy, immunotherapy, or other types of drugs.  

Once you've figured out the specific type of metastatic breast cancer, the treatment approach is slightly different. "Because we can't cure metastatic breast cancer, quality of life and quantity of life are important goals," says Dr. Montero. "We try to utilize treatments that will control cancer but at the least amount of toxicity." For example, in the case of estrogen-positive cancer, he says doctors will try to maximize anti-estrogen therapies to control the cancer before moving onto chemotherapy, because the estrogen drugs have fewer side effects. This allows patients to make the most out of their lives. 

Dr. Montero says that many patients assume that the more side effects a treatment has, the more effective it is. That's a common misconception, he says. Hormone therapies can be incredibly effective for estrogen-positive cancers, as are antibody treatments for HER2-positive cancers—and with far fewer side effects than conventional chemotherapy. 

"We also work closely together with palliative medicine doctors," says Dr. Montero. These are doctors trained specifically to help patients manage side effects from their cancer treatment or other cancer-related issues. Working with palliative medicine experts can help increase a patient's quantity and quality of life, he says. Indeed, a 2021 review of studies in the journal Health Care for Women International concluded that palliative care "is fundamentally important to alleviate pain and distress among patients with [metastatic breast cancer]."

What is the prognosis of metastatic breast cancer?

According to the American Cancer Society, the relative five-year survival rate for metastatic breast cancer is 28%. This means that on average, just 28% of patients diagnosed with metastatic breast cancer are still alive five years after diagnosis. 

However, survival rate is impacted by many different factors, says Dr. Taiwo. Age of diagnosis, the specific type of breast cancer and where it has spread, and a person's age when they're diagnosed with metastatic breast cancer can all impact how long they live. How the cancer responds to treatment plays a significant role, too. Some people only survive for a short time, while she says others can live well beyond the five-year mark. 

Thankfully, survival rates have generally improved thanks to better treatment options. "We have patients living for up to 10 years," Dr. Taiwo says. The numbers might look grim, but there is still plenty of room for hope with a metastatic breast cancer diagnosis with the right treatment protocol and medical team.

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