Metastatic Breast Cancer in Bones: Treatments and Survival Rates

Breast cancer impacts millions of people every year. But metastatic breast cancer—breast cancer that has spread to other body parts—is less common. Only about 30% of people who have breast cancer later develop metastatic disease.

While breast cancer can spread anywhere, "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.

In fact, 70% of breast cancer patients who later develop stage 4 cancer have bone metastases, according to 2017 data.

But 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.

What Is Metastatic Breast Cancer in Bones?

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

Metastatic breast cancer in the bone can happen when cancer returns after treatment—also called recurrent cancer. It can also occur because your cancer didn't respond to treatment or wasn't treated in time.

Researchers don't understand precisely how cancers metastasize, said Nancy Lin, MD, a medical oncologist specializing in breast cancer treatment at Dana-Farber Cancer Institute in Boston.

"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," said Dr. Lin. Beyond that, it's unclear why certain cancers spread to specific spots, but there are some theories.

Evelyn Toyin Taiwo, MD, hematologist and oncologist at Weill Cornell Medicine in New York, theorized that some breast cancer types could spread to the bone because it has estrogen receptors. The presence of estrogen receptors might provide a favorable environment for rogue cancer cells to grow. Still, 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:

• Hips 
• Femur
• Upper arm
• Ribs
• Skull

Metastatic Breast Cancer in Bones Symptoms

All three healthcare providers said that new, progressive pain in your 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, Tsarwhas added. So, people 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, Dr. Tsarwhas added. 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," Tsarwhas said.

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

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

Metastatic Breast Cancer in Bones Treatments

Metastatic breast cancer in the bones is typically not curable. Dr. Taiwo said that healthcare providers instead focus on slowing cancer growth and managing symptoms.

"The focus really is trying to extend life and maintain quality of life," explained Dr. Taiwo.

Healthcare professionals usually prescribe traditional medications like chemotherapy and immunotherapy. They'll also try targeted treatments for specific cancer types. For example, they may use hormone treatments for estrogen receptor-positive breast cancer, added Dr. Tsarwhas.

But many bone-strengthening medications help people, like Prolia (denosumab). Those medications help slow bone degradation and reduce the risk of fractures, Dr. Tsarwhas said.

Dr. Lin added that many of the treatments are similar to what people with osteoporosis take.

Localized radiation treatment can also help shrink bone cancer cells and reduce pain. Dr. Taiwo said that treatment could improve a patient'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," Dr. Lin added. In those cases, Dr. Lin said healthcare providers often send people to orthopedic surgeons for preventative surgeries to help stabilize bones.

For example, surgeons can use medical-grade bone cement to seal and support existing fractures. Or they may recommend joint-replacement surgery to ensure a person has pain-free mobility.

Breast Cancer Metastasis to Bone 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 for people with metastatic breast cancer is about 29%.

That means people with metastatic breast cancer are about 29% as likely to be alive five years after diagnosis as people who don't have that cancer.

However, some evidence shows that metastatic breast cancer in the bones seems to have one of the best survival rates compared to other types of metastatic breast cancer.

A 2019 study published in the journal BMC Cancer looked at five years of data to track the survival rates of stage four breast cancer patients and calculated specific rates based on the site of metastasis.

The researchers found that patients with bone metastasis had the best overall survival (OS) rate, with 50.5% surviving for over three years.

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

Other research published in BMJ Open estimated that the one-year survival rate of metastatic breast cancer in the bones is 51%. And the five-year survival rate is 13%. But those numbers are estimates, not foregone conclusions.

A lot of factors can impact a person's prognosis, said Dr. Lin, including:

• The type of cancer they have
• Where cancerous cells spread
• Their age
• Any other pre-existing conditions or health problems

And some cancers respond better to treatment than others, which can positively affect a person's survival.

Overall, treatment and life expectancy for metastatic breast cancer has 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. Still, they can significantly improve the length and quality of a patient's life—which is the next best thing.

A Quick Review

Breast cancer can sometimes spread from your breast area into your bones—also called metastatic breast cancer. When cancerous cells make it to your bones, they can cause symptoms like new bone pain.

There's no cure for metastatic breast cancer in the bone. But your healthcare provider can offer many options to treat symptoms, slow the spread of your cancer, and prolong your life.

The five-year survival rate is estimated to be about 29%. However, many factors can impact a person's prognosis.