Metastatic breast cancer in the bone

When breast cancer spreads to the bones, it is called metastatic breast cancer in the bone, not bone cancer.

Doctors treat it with breast cancer drugs, not treatment for a cancer that began in the bones.

The bone is the most common site for metastases. Metastatic breast cancer deposits in the bone are called ‘bone metastases’ or ‘bone secondaries’.

See About metastatic breast cancer to understand how and why it develops.

Common places for bone metastases

When metastatic breast cancer spreads to the bone, it appears most often in:

• ribs
• spine
• skull
• pelvis
• upper bones of the arms and legs.

If there is a lot of cancer in the bones, it can sometimes affect the bone marrow. 

Symptoms of bone metastases

Signs that you may have metastatic breast cancer in the bone vary. It depends on where the metastases are, and their size.

Common symptoms are pain, fatigue and weakness. You may experience one or more of these symptoms, or none at all.

Bone pain

Often, the first symptom of bone metastases is bone pain, particularly in the back, arms or legs. It can be difficult to know what is causing pain as it might be muscular or the result of arthritis.

However, pain from cancer in the bone usually develops into a constant ache. This may be worse when you’re active. It generally doesn’t go away at night so you could find it difficult to sleep.

Fracture (broken bone)

If you have a sudden severe pain or are not able to move, you may have a fracture or broken bone. Cancer in the bone can erode and weaken bones and cause them to fracture or break.

Low blood cell count

The bone marrow is where blood cells are made. If the bone marrow is affected by metastatic breast cancer, you may have low levels of:

• red cells (‘anaemia’)
• white cells (reduced ability to fight infection)
• platelets (bruising or bleeding).

The low blood count may show up on a routine blood test.

Hypercalcemia

Metastatic breast cancer in the bones can cause calcium to be released into the bloodstream. This is called hypercalcaemia.

While hypercalcemia is uncommon, you should seek medical assistance straight away if you think you have symptoms.

Symptoms of hypercalcaemia may include:

• loss of appetite
• nausea and vomiting
• constipation
• increased thirst
• frequent urination
• difficulty concentrating
• drowsiness and confusion.

Spinal cord compression

Cancer in the bones of the spine (‘vertebrae’) can cause pressure on a nerve or the spinal cord. This is called spinal cord compression.

This is rare, but it is a medical emergency and you should seek medical assistance immediately. Do not wait until the next day to seek treatment. Out-of-hours, phone the emergency number your treating team gave you or go to your local hospital emergency department.

Symptoms of pressure on the spinal cord may include:

• severe or sudden back pain
• difficulty walking
• numbness or weakness in the legs
• problems passing urine (difficulty controlling your bladder, passing very little urine or passing none at all)
• change in bowel habits (constipation or trouble controlling bowel motions).

How metastatic breast cancer affects bones

Bone contains two types of living cells – osteoclasts and osteoblasts – as well as calcium, other minerals and proteins.

• osteoclasts destroy and remove small amounts of old or damaged bone
• osteoblasts build new bone to replace the old or damaged bone.

When bone is healthy, these two activities are in balance. Our bones break down and rebuild constantly.

In metastatic breast cancer, the cancer cells that have spread to the bone produce chemicals that disrupt this balance.

Two types of metastases affect bones. They both leave the bone weak and fragile.

1. Osteolytic tumours break down bone and can create holes
2. Osteoblastic tumours cause new bone to form abnormally.

Cancer cells may also grow in the bone marrow. This is a material like a sponge in the centre of the bone, where blood cells are made. When cancer cells grow, it is harder for the bone marrow to make enough blood cells.

This can lead to low blood counts (red blood cells, white blood cells and platelets). Low blood counts can lead to:

• anaemia
• increased risk of infection
• bruising
• bleeding.

Once treatment starts to be effective and the number of cancer cells in the bone marrow decreases, blood counts can start to return to normal.

The diagram below shows the build-up of cancer cells in the bone marrow. Before treatment, this build-up affects the marrow's ability to make new blood cells.

After treatment, chemotherapy has made the cancer smaller and the marrow returns to normal.

Treatment for metastatic cancer in the bone

Metastatic breast cancer in the bone can be treated and, in many cases, controlled for long periods. While it can’t be cured, many people with bone metastases live for many years and enjoy good quality of life.

Treatments for bone metastases are often very effective at stopping the growth and/or decreasing the size of the cancer deposits in the bone.

Resources

The Metastatic breast cancer in the bone booklet is part of our Hope and Hurdles resource. Hope and Hurdles includes a longer Information Guide about living with metastatic breast cancer. This can help you make informed decisions about your individual treatment, care and wellbeing.

Video: Understanding and managing pain with metastatic breast cancer

Medical oncologist Dr Belinda Yeo talks about the different types of pain and ways to explain your type of pain to your treating team. She shares information about current therapies, and strategies to help maintain quality of life when living with pain associated with metastatic breast cancer.
This video is part of our 'Ask the expert’ series and was recorded in July 2023.

Video: New and emerging treatments for metastatic breast cancer

Gill Kruss, a metastatic breast care Nurse Practitioner, hosts this session with medical oncologist Dr Nick Zdenkowski and BCNA Consumer Representative Kim Parish. They explore the importance and availability of clinical trials that find new and/or better cancer treatments that might extend or improve quality of life.

Conference: Thriving Together – Living Longer, Living Stronger
This 2021 conference explores:

• treatments on the horizon for metastatic breast cancer
• the management of bone metastases
• the importance of connecting with others for support to enhance control and reduce feelings of isolation and loneliness 
• strategies to help you with ‘living’ with metastatic breast cancer.