There are rarely ever any "upsides" to a cancer diagnosis. But in the case of breast cancer, there's at least the reassuring fact that survival rates tend to be incredibly high—a 90% five-year survival rate when averaging together all stages of breast cancer, per the American Cancer Society (ACS).
When you break down life expectancy by stage of breast cancer, that's where things get trickier. While earlier-stage breast cancer patients tend to have an incredibly high survival rate (up to 99%, per the ACS), people with metastatic breast cancer have a very different numbers game.
But experts say it's not all bad news for people with metastatic breast cancer. Here's what to know about the metastatic breast cancer survival rate, how prognoses can vary drastically between patients, and what treatments to expect if you have the disease.
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What is metastatic breast cancer?
Metastatic breast cancer (also known as stage 4 breast cancer), is breast cancer that has spread beyond the breast and the surrounding lymph nodes to other parts of the body, Nancy Lin, MD, an oncologist who specializes in breast cancer at Dana-Farber Cancer Institute in Boston, tells Health. Approximately 30% of breast cancer patients will develop metastatic breast cancer following an initial earlier-stage diagnosis, according to a review in the Journal of Internal Medicine. Meanwhile, the American Society of Clinical Oncology says just 6% of women have metastatic breast cancer when they are first diagnosed.
"Basically what's happening is the cancer cells are growing…they get into the bloodstream which then allows them to travel to distant sites [in the body]," Evelyn Toyin Taiwo, MD, hematologist and oncologist at Weill Cornell Medicine and NewYork-Presbyterian Brooklyn Methodist Hospital, tells Health. Metastatic breast cancer cells most often take up residence in the bones, liver, lungs, and brain, she says, but they can spread anywhere in the body.
It's still unclear to science how or why certain cancers metastasize and others don't, says Dr. Lin, or why breast cancer cells seem to prefer spreading to those specific regions of the body. The type of cancer may play a role in where it metastasizes. For example, Dr. Lin says triple-negative breast cancer seems to often spread to the lungs, while estrogen-receptor (ER) positive breast cancer often spreads to the bones.
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What is the prognosis or life expectancy of metastatic breast cancer?
Metastatic breast cancer is the most advanced stage of breast cancer, and there is no cure for it, says Dr. Lin. According to the ACS, the five-year survival rate for people with breast cancer that has spread beyond the breast and surrounding lymph nodes is 28%—that means women with this form of breast cancer are just 28% as likely to be alive five years from diagnosis as women who do not have cancer.
This may sound grim, but there are a few important things to keep in mind about survival rates. First off, there is a lot of variability between patients, because survival is affected by many different factors. All of the following can impact a metastatic breast cancer patient's survival, says Dr. Taiwo:
- Age at diagnosis
- Other existing medical conditions they have
- The specific type of breast cancer (such as triple-negative or HER2-positive)
- Where the cancer spread in the body (bones, lungs, liver, brain, or elsewhere), and how extensive it is
- How the cancer responds to treatment
For example, Dr. Taiwo says that the life expectancy of a metastatic breast cancer patient who has been on the same treatment for three years is likely going to be better than a patient who had to change treatments a few times because their cancer isn't responding to it. Similarly, a patient who has one bone lesion (meaning cancer site) will likely fare better than a patient whose cancer has spread to multiple sites in their bones as well as their lungs or liver.
Additionally, Dr. Lin says, official metastatic breast cancer survival rates can be misleading. They're averages, which don't really factor in all of the above-mentioned nuances that can impact life expectancy. "The average includes all the people who do worse than the average, and all the people who do better," she says. Some people might live for 20 years with metastatic breast cancer, she says, while others might only live for a year or so.
How the survival rate is calculated also matters. If the survival rate is based on data from the National Cancer Institute's Surveillance, Epidemiology, and End Results program (SEER)—a program run by the National Institutes of Health that tracks cancer data and outcomes for millions of patients—then Dr. Lin says it's only factoring in people with a specific type of metastatic breast cancer. "When [SEER] looks at metastatic breast cancer…it's in people who were stage 4 from the very beginning," she says. But most stage 4 breast cancer patients become metastatic after another initial diagnosis and treatment program, making the survival rates of these other folks not quite as applicable. That's why Dr. Lin often relies on clinical trial data for better estimates, since those trials tend to include other types of metastatic breast cancer patients. (Note: This isn't to say that SEER data is bad or inaccurate. SEER plays a critical role in helping provide researchers with tons of data on cancer patients to help inform treatment, care, and more.)
Another factor to consider: Survival rates generally tend to be a tad outdated, Dr. Lin says. "If you want to know the chance of being alive five years from a metastatic diagnosis, you have to go back at least five years to look at patients who started with their metastatic disease [at that time]. That means some of the treatments that are available now would not have been available to the patients who we're following from five years ago," she says, which absolutely impacts a person's chances for survival.
The good news: "There's been significant progress in terms of survival [from metastatic breast cancer]," says Dr. Taiwo, especially since the early '90s. Indeed, a 2018 meta-analysis published in JNCI Cancer Spectrum found that the average life expectancy from metastatic breast cancer increased from 21 months (slightly less than two years) to 38 months (just over three years) between 1990 and 2010. That number has very likely improved since then thanks to better treatments available.
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How can treatment options help metastatic breast cancer?
As mentioned, metastatic breast cancer is not curable. But there are many treatments available to help extend a patient's life, both experts say.
"The goal of treatment is controlling the disease," says Dr. Taiwo. "If we're able to control disease growth, we're also then able to control symptoms." This, in turn, improves the quality of life for the patient so that they can live with the disease for as long as possible without dramatically altering their day-to-day functioning.
As with an earlier-stage breast cancer, there are lots of treatments available for managing metastatic breast cancer. Chemotherapy is one common option, says Dr. Lin, particularly for metastatic triple-negative breast cancer. For people who have a hormone-receptor positive breast cancer (such as ER-positive breast cancer) that has metastasized, targeted hormone therapies are often used to slow the growth of tumors. Some people might also receive immunotherapy, which works to help a patient's immune system target and destroy cancer cells.
Treatment often can target site-specific symptoms, adds Dr. Taiwo. For example, she often uses radiation treatment to help manage pain caused by metastatic bone lesions. Medicines to strengthen the bones (similar to what's used to treat osteoporosis) can also help people whose cancer spread to their bones, says Dr. Lin.
The bottom line: While the metastatic breast cancer life expectancy doesn't seem like a happy picture, treatments and care advancements have come a long way in recent decades to improve patients' odds significantly. "It's important with the fear that comes with the diagnosis of a stage 4 cancer to sort of also feel empowered that there are tons of treatments out there," says Dr. Taiwo. "We're definitely making strides in improving care, so survival now in 2021 is probably going to be very different five years from now."
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