Metastatic Breast Cancer in Bones: Treatments and Survival Rates

Breast cancer impacts millions of people every year. Metastatic breast cancer, or breast cancer that's spread to other body parts, is less common. Only about 20% to 30% of people who have breast cancer later develop metastatic disease.

Breast cancer can spread anywhere, but "the most common area for breast cancer to metastasize to is the bones," Dean Tsarwhas, MD, head of the oncology program at Northwestern Medicine Lake Forest Hospital, told Health. About 70% of those with breast cancer who later develop stage 4 cancer have bone metastases.

What are the implications of metastatic breast cancer in the bones, and how does that affect a person's treatment and prognosis? According to oncologists, here's everything you need to know about metastatic breast cancer in the bones.

What Causes Breast Cancer To Spread?

Metastatic breast cancer is when cancer cells spread beyond the breast and the surrounding lymph nodes to other body parts. Cancer cells spread to your skeletal system and move into parts of your bone, replacing healthy cells with cancer cells. Cancerous lesions, or tumors, later form.

Metastatic breast cancer in the bone can happen when cancer returns after treatment, which is also called recurrent cancer. It can also occur if cancer doesn't respond to treatment or isn't treated in time.

Researchers don't precisely understand how cancers metastasize. "We know that at some point, the cancer manages to find its way into the bloodstream and then through that, is able to get to other parts of the body," Nancy Lin, MD, a medical oncologist specializing in breast cancer treatment at Dana-Farber Cancer Institute, told Health.

It's unclear why certain cancers spread to specific spots, but some theories exist. Evelyn Toyin Taiwo, MD, hematologist and oncologist at Weill Cornell Medicine, theorized that some breast cancer types could spread to the bone if they have estrogen receptors. The presence of estrogen receptors might provide a favorable environment for rogue cancer cells to grow. More research is needed to understand the link.

Metastatic cancer can affect any part of your skeletal system, but the spine is the most common site. Other areas include:

• Femur
• Hips 
• Ribs
• Skull
• Upper arm

Signs of Metastatic Breast Cancer in Bones

All three healthcare providers said new, progressive pain in the bones or joints is one of the most common symptoms of metastatic breast cancer in the bone. "I always tell patients to inform me if there's pain that's not getting better," said Dr. Tsarwhas.

People can sometimes confuse the pain with arthritis or other pre-existing chronic pain issues. Those with breast cancer must be proactive about any new pain they encounter. New fractures or unexplained fractures can also be a sign of bone metastasis. Cancer can weaken bones and make them break more easily than usual.

"New lumps or bumps in the lymph node area could be a sign of recurrent breast cancer, as well," said Dr. Tsarwhas.

People with metastatic breast cancer in their bones may also experience more general cancer symptoms, such as:

• Extreme, unexplained weight loss
• Fatigue
• Lack of appetite
  

Treatments for Bone Metastases

Metastatic breast cancer in the bones is typically not curable. Healthcare providers typically focus on slowing cancer growth and managing symptoms. "The focus really is trying to extend life and maintain quality of life," said Dr. Taiwo.

Healthcare providers usually prescribe traditional medications like chemotherapy and immunotherapy. They'll also try targeted treatments for specific cancer types, such as hormone therapy for estrogen receptor-positive breast cancer.

Many bone-strengthening medications, like Prolia (denosumab), can help. These medications slow bone degradation and reduce the risk of fractures. Many of the treatments are similar to those for people with osteoporosis.

Localized radiation treatment can also help shrink bone cancer cells and reduce pain. Treatment could improve a person's quality of life since bone lesions can be painful.

"We also look for any bones that might have the potential to cause a problem in terms of a fracture," said Dr. Lin. Healthcare providers often send people to orthopedic surgeons for preventative surgeries to stabilize bones in these cases.

Surgeons can use medical-grade bone cement to seal and support existing fractures. They may also recommend joint-replacement surgery to ensure a person has pain-free mobility.

Prognosis and Life Expectancy

Metastatic breast cancer in the bones prognosis typically isn't as favorable as early-stage breast cancers. The five-year relative survival rate is about 29%. This means people with metastatic breast cancer are about 29% as likely to be alive five years after diagnosis as those who don't have this cancer.

Some evidence suggests that metastatic breast cancer in the bones seems to have one of the best survival rates compared to other types. A study published in 2019 looked at five years of data to track the survival rates of people with stage 4 breast cancer. The researchers calculated specific rates based on the site of metastasis. They found that those with bone metastases had the best overall survival (OS) rate, with 50.5% surviving for over three years.

People with brain metastases had a three-year OS rate of 19.9%. Those with liver and lung metastasis had a three-year OS rate of 38.2% and 37.5%, respectively.

Other research has estimated that the one-year survival rate of metastatic breast cancer in the bones is 51%. The five-year survival rate is 13%. Keep in mind that these numbers are estimates, not foregone conclusions.

Some cancers respond better to treatment than others, which can positively affect a person's survival. Other factors can impact a person's prognosis, such as:

• Age
• Any other pre-existing conditions or health concerns
• The type of cancer they have
• Where cancer cells spread

Treatment and life expectancy for metastatic breast cancer have improved drastically along with developments in treatments. "We have many more options for [metastatic] cancer patients living longer," said Dr. Tsarwhas. The existing drugs and therapies can't cure it, but they can significantly improve the length and quality of a person's life.

A Quick Review

Breast cancer can sometimes spread from the breast area into the bones, which is also called metastatic breast cancer. Cancer cells can cause new symptoms like bone pain if they make it to the bones.

There's no cure for metastatic breast cancer in the bones. A healthcare provider can still offer many options to treat symptoms, slow the spread of cancer, and prolong life. The five-year survival rate is estimated to be about 29%, but many factors can impact prognosis.