Where Breast Cancer Can Spread

Breast cancer has one main intention—to spread. Often, the first stop is the lymph nodes. And, as it advances, metastases can occur in distant parts of the body, some of the most common ones being the bones, lungs, liver, and brain. The areas to which breast cancer spreads, and the extent to which it does, are important as metastasis is responsible for most deaths from the disease.

Doctors aren't certain why cancer recurs and spreads, or how it can appear to lie dormant for years and even decades and then recur. Much research is being conducted to look at why metastases occur, as well as methods that might inhibit the spread of breast cancer to other parts of the body.

Common Sites of Metastasis

The areas of the body to which breast cancer spreads vary. The most common sites include:

• Lymph nodes
• Bones
• Lungs
• Liver
• Brain
• Peritoneal cavity (pelvis and abdomen)

A 2013 study looked at the most common first site of metastases in women with early-stage breast cancer. The frequencies were:

• Bones: 41%
• Lungs: 22%
• Liver: 7.3%
• Brain: 7.3%
• All less common sites: 22.4%

Invasive lobular carcinoma tends to have a significantly different pattern of metastases than ductal breast cancer. In one 2017 study, almost 70% of people with metastases from lobular carcinoma had peritoneal metastases.

For roughly a third of women (and men, as men get breast cancer too), cancer spreads to multiple organs at the same time.

How Breast Cancer Spreads

Breast cancer can spread through the lymphatic system, the bloodstream, or by local invasion—for instance, when cancer cells actually invade nearby tissues, such as the chest wall or ribs.

When breast cancers spread and enter the lymphatic system, they usually first arrive at nearby lymph nodes and may still be early-stage.

Metastatic breast cancer is the same thing as stage 4 breast cancer and is considered the most advanced stage. It refers to breast cancers that have spread beyond the breast and nearby lymph nodes to other regions of the body, which are called distant metastases.

While treatment options for metastatic breast cancer are similar no matter where cancer has spread, some treatments are used for specific sites of metastasis as well (see below).

Recurring Cancer

Metastasis may occur months, years, or even decades after the original tumor was detected and treated; some cancer cells can survive and lie dormant, waiting to grow at a later time. A recurrence can be local (at the original tumor site), regional (lymph nodes), or distant (other areas of the body).

Lymph Node Metastases

The spread of breast cancer to lymph nodes does not necessarily mean that it's metastatic, even though a pathology report may state "breast cancer metastatic to lymph nodes." When cancer recurs in a lymph node near the breast, it is considered a regional recurrence and not a distant recurrence.

Lymph-node positive breast cancer can be stage II, III, or IV. Breast cancer reaching the lymph nodes is its declaration that it's working to spread further.

Oligometastases

Metastasis to a limited number of sites is called oligometastasis. In these cases (which may involve one or more of the below locations in the body), stereotactic body radiotherapy (SBRT) may be used in an attempt to destroy the metastasis completely. SBRT, also known as Cyberknife or gamma knife, is a procedure in which high doses of radiation are delivered to a small and very precise area of tissue over several sessions. You may also hear this referred to as local ablation.

The treatment of oligometastases is a relatively new approach in oncology, and few studies had been done to evaluate the potential survival benefit. A 2019 study, however, looked at survival in people with a few different types of cancer who had local treatment for up to five metastases (in the same region or different regions). They found that treating these oligometastases significantly improved overall survival.

Bone Metastases

The most common site of distant breast cancer metastases, occurring in around 70% of people with metastatic breast cancer, is the bones. The ones most commonly affected include:

• Spine
• Ribs
• Pelvis
• The long bones of the arms and legs

Bone metastases tend to have a fairly good prognosis relative to metastases to some other regions of the body.

Symptoms and Detection

While bone metastasis may cause pain, that is not always the case. Some people are unaware that they have bone metastasis until they suffer a fracture from what should've been a minor trauma. Fractures through a portion of a bone weakened by cancer metastasis are called pathologic fractures.

If not detected as the result of evaluating a fracture, breast cancer that has spread to the bones may be found on a routine scan done to look for such metastases (when no symptoms are present) or on scans that are done to evaluate symptoms.

Treatment

Several types of treatment are available for bone metastases from breast cancer, and some of these can control the disease for quite some time.

• Radiation therapy is often done when rapid relief is needed, and it can be very effective for the local treatment of bone metastases.
• Drugs such as Strontium 89 include a particle of radiation attached to another chemical that is injected into the bloodstream. These treatments, in contrast to radiation therapy, are often effective when a person has multiple or widespread bone metastases.
• Sometimes surgery is needed to stabilize a bone that has fractured or is at risk of fracturing due to metastases. When bone metastases occur in the spine, they can sometimes lead to spinal cord compression, a condition that requires immediate attention to prevent paralysis and more.
• Bone-modifying medications are a newer treatment for bone metastases and can be very effective. Bisphosphonates such as Zometa (zoledronic acid) are not only effective in reducing pain from metastases but appear to have anti-cancer effects as well. These medications may also reduce the chance of further bone metastases and improve survival. Xgeva (denosumab) may also be effective in treating bone metastases while improving survival.

Liver Metastases

Breast cancer metastases to the liver are also very common. Treating them is often complicated.

Symptoms and Detection

Liver metastases may be present without any symptoms. If symptoms do occur, they can include:

• Abdominal pain
• Nausea
• Itching (which can be severe)
• Jaundice (a yellowish discoloration of the skin and the whites of the eyes)

Sometimes, liver metastases are suspected based on abnormal liver function tests. Liver metastases are often detected on tests such as a positron emission tomography (PET) scan.

Treatment

General treatments for metastatic cancer (such as chemotherapy, hormonal therapies, and targeted therapies) may decrease these metastases, but since the liver acts as the detoxification center of the body, treatments must be delicately balanced. Sometimes, liver metastases reduce the ability to tolerate chemotherapy.

Radiation therapy to the liver can decrease pain and may improve survival.

At times, other local treatments may be used to treat liver metastases such as surgery, radioembolization, chemoembolization, radiofrequency ablation, or stereotactic body radiotherapy.

Lung Metastases

Just as the blood is filtered by the liver, blood passes through the lungs, making this a common site of breast cancer metastasis.

Symptoms and Detection

The most common symptom of lung metastases is shortness of breath, which may be mild and only occur with exercise at first. Other symptoms can include a persistent cough or pain with breathing.

Lung metastases may be suspected based on a scan, which often shows multiple small areas of metastases (in contrast to lung cancer, for example, which is more likely to appear as a single large mass).

In addition to spreading to the lungs, metastatic breast cancer often causes pleural effusions—a build-up of fluid in the space between the membranes (the pleura), which line the lungs. Pleural effusions occur not only when breast cancer spreads to the lungs, but with spread to the lymph nodes in the area between the lungs (the mediastinum).

The fluid may be benign (without cancer cells) and related to inflammatory changes, or instead, contain cancer cells (malignant pleural effusion).

Treatment

Lung metastases are often treated by the general treatments for metastatic breast cancer, but radiation therapy may be helpful, especially if the metastases cause an obstruction in the airways (bronchi). If only a few metastases are present, treatment to eradicate these may be considered.

Before treatment, however, it's important to make sure that a nodule in the lung is, indeed, due to breast cancer. Primary lung cancer is treated differently than breast cancer that spreads to the lungs.

Pleural effusions can be quite large and cause significant shortness of breath. The fluid is often removed by placing a needle through the chest wall and into the pleural cavity to drain the fluid. Unfortunately, pleural effusions often recur. When this happens, a shunt may be placed, or pleurodesis recommended (a procedure in which the layers of the pleura are scarred together so fluid cannot reaccumulate).

Brain Metastases

Breast cancer spreads to the brain in about 10% to 15% of people with metastatic breast cancer overall. Brain metastases are more common in women with HER2-positive tumors and triple-negative breast cancer, with brain metastases occurring in roughly a third of people with HER2-positive breast cancers that metastasize.

Symptoms and Detection

Symptoms of brain metastases often include:

• Headaches
• Visual changes
• Dizziness
• Seizures (sometimes a seizure is the first symptom)

Other symptoms may include:

• Weakness on one side of the body
• Problems with coordination
• Personality changes

Not everyone with brain metastases has symptoms, though. Sometimes, they're only found because of imaging tests performed on the brain.

Treatment

Unlike metastases to some other regions, treatments such as chemotherapy and targeted therapies are often ineffective against brain metastases due to the blood-brain barrier, which is a tight network of capillaries designed to protect the brain from toxins (such as chemotherapy).

The treatment of metastases usually includes steroids to decrease swelling in the brain. Whole-brain radiation may be used to address the metastases, along with medication to reduce the risk of cognitive problems thereafter.

Leptomeningeal Metastases

Leptomeningeal metastases, also called carcinomatous meningitis, differ from brain metastases in that the cancer cells spread to the cerebrospinal fluid that bathes the brain and spinal cord. Since cancer cells float freely in the space between the leptomeninges (the subarachnoid space), they have constant access to nutrition and don't usually form a discreet mass.

Leptomeningeal metastases often occur late in the disease but are becoming more common as people live longer with metastatic cancer.

Treatment often involves injecting chemotherapy directly into this space (intrathecal chemotherapy).

Less Common Sites of Distant Metastases

Breast cancer can spread to nearly any region of the body. Some of the less common sites (with the exception of lobular carcinoma) of metastasis include:

• Bone marrow
• Peritoneal metastases (accounting for two-thirds of people with metastatic lobular carcinoma)
• The opposite breast
• An ovary
• Adrenal glands
• Pancreas
• Skin and soft tissue