Here are the systemic and localized symptoms that usually make doctors take notice.

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Breast cancer is the second most common type of cancer among women in America, according to the American Cancer Society (ACS). One in eight women will develop the disease at some point in their lives.

For the most part, breast cancer in general is very treatable if detected early. But sometimes, that cancer can spread to distant parts of the body—places beyond the breast and nearby lymph nodes—and become too advanced to treat with the intent of a cure. This is known as metastatic breast cancer, or stage 4 breast cancer, and it's the most advanced stage of the disease.

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Credit: Getty Images

The most common places for breast cancer to spread are the bones, liver, lungs, and brain; and less commonly, to the abdomen and skin, Nancy Lin, MD, an oncologist who specializes in breast cancer at Dana-Farber Cancer Institute in Boston, tells Health. Experts aren't entirely sure why or how breast cancer spreads in this way, but per the National Cancer Institute (NCI), metastasis occurs when cancer cells find their way into the blood stream and lymphatic system and thus are able to move throughout the body.

Where, exactly, breast cancer metastasizes to matters a lot regarding how symptoms in stage 4 cancer present—the signs of metastatic breast cancer can vary significantly depending on where it has spread and how far it has progressed. Here, experts break down the many metastatic breast cancer symptoms, and what to know if you or a loved one are experiencing them.

What are the systemic symptoms of metastatic breast cancer? 

As with any cancer that has progressed throughout the body, there are some systemic, or full-body symptoms of metastatic breast cancer. However, because these symptoms also overlap with symptoms of many other health conditions, it's best to consult with your doctor before jumping to any conclusions to ensure you get proper treatment. 

In the case of metastatic breast cancer, these systemic symptoms are a result of your cancer cells starving your body of nutrients. "When you have metastatic disease, the body is really competing with the cancer for survival, nutrition, and energy," Evelyn Toyin Taiwo, MD, hematologist and oncologist at Weill Cornell Medicine and NewYork-Presbyterian Brooklyn Methodist Hospital, tells Health. "The body has to work a little bit harder than it normally does [to function." Here are some of the more common full-body symptoms of metastatic breast cancer:

Fatigue

This is a common cancer symptom in general, and can be a sign that a person's cancer has metastasized. As mentioned, cancer cells rob healthy cells of nutrients in order to grow; this starves your cells and contributes to feeling tired, according to Johns Hopkins Medicine. Cancer can also cause anemia, a condition in which a person lacks enough healthy red blood cells, says Dr. Taiwo, which can also affect energy levels.

Lack of appetite

According to Dr. Taiwo, anorexia (which in this case means lack of appetite) is a common symptom of metastatic cancer. If a person is experiencing other site-specific symptoms of their cancer like nausea or vomiting (more on those in a minute), they might not want to or be able to eat as much. Per the ACS, certain types of cancers might also release hormones that impact a person's natural hunger signals. 

Extreme weight loss

This again goes back to the fact that cancer is starving your healthy cells of nutrients. When a cancer has progressed to the point of metastasis, a person can start losing weight without intending to. Additionally, a person who doesn't eat due to lack of appetite will eventually start to lose weight.

What are the localized symptoms of metastatic breast cancer?

Metastatic breast cancer most often spreads to the bones, lungs, liver, and brain. It doesn't spread exclusively to those locations, but these are the most common sites of metastasis.

Most metastatic breast cancer patients don't experience symptoms in their breasts, says Dr. Taiwo. That's because in the majority of cases of metastatic breast cancer, a person was previously diagnosed with an earlier-stage breast cancer and received localized treatment to their breasts. Only a minority of metastatic breast cancer patients are initially diagnosed with stage 4 cancer; if they have a breast mass, it likely isn't painful, she says. Very rarely does a breast cancer mass grow to the point where it becomes ulcerous and painful. 

Thus, most symptoms of metastatic breast cancer vary depending on where the cancer has spread. Someone who has cancerous lesions in their bone will have a different set of symptoms than someone whose cancer has metastasized to their brain or liver. Here's an overview of the different symptoms for these common sites. 

Metastatic breast cancer symptoms in the bones: 

The bone is one of the most common places for breast cancer to metastasize—60% of metastatic breast cancer patients experience bone or lung metastasis, according to research published in the journal Cancer. The most common symptom is bone or joint pain that progressively gets worse, Dean Tsarwhas, MD, the medical director of cancer services for Northwestern Medicine Lake Forest Hospital, tells Health. Dr. Taiwo adds that the most common areas for bone to be affected are in the hip and lower back.

Identifying bone pain can be challenging for patients who have arthritis or other chronic pain issues, Dr. Taiwo says. "Patients who have arthritis...aren't that concerned about the pain that they're having. They think it's part of the arthritis." She says that any new pain that feels different than other chronic pain a patient may have experienced is a red flag that their breast cancer may have spread.

In rare cases, Dr. Taiwo says that patients find out they have metastatic breast cancer in their bones after breaking their bone (say from a fall or other injury). "In the process, images are done and we find that they have other [bone] lesions in the area." This is known as a pathologic fracture.

Metastatic breast cancer symptoms in the liver: 

This can be a bit trickier to identify because the symptoms can be similar to other stomach and gastrointestinal issues, says Dr. Taiwo. Often a person will have abdominal pain, nausea, and vomiting, or even jaundice (where the skin and whites of the eyes turn yellow), depending on how much the cancer has spread in the liver. By the time that a patient tends to present with symptoms, they already have a fairly significant burden of disease, she says—meaning that their cancer has already progressed to make them very sick. 

Metastatic breast cancer symptoms in the lungs: 

As with the liver, there aren't often symptoms of metastatic breast cancer in the lungs until the disease has progressed fairly significantly, says Dr. Taiwo. Sometimes a person has a dry cough, or fluid builds up in the lungs to cause shortness of breath

Metastatic breast cancer symptoms in the brain: 

Metastatic breast cancer doesn't often spread to the brain, although it is more common with triple-negative breast cancer, says Dr. Tsarwhas. When it does, symptoms can include headaches, nausea, vomiting, dizziness, or trouble standing or walking, says Dr. Taiwo. In rarer cases, a patient can experience seizures. These symptoms result from the increased intracranial pressure caused by addition of cancer to the brain cavity—which is a pretty tight space to begin with, Dr. Taiwo says. 

What are the symptoms of metastatic breast cancer complications?

If a person's cancer has progressed significantly without treatment (or without response to treatment), it can cause more serious complications that can be life threatening. Here are some of the most common: 

Bone fractures

These are a common complication from metastatic breast cancer that has spread to the bones, Alberto Montero, MD, director of the breast cancer program at University Hospitals Seidman Cancer Center in Cleveland, Ohio, tells Health. "Cancer in the bone can erode the integrity of the bone, causing a fracture," he says. 

Spinal cord compression

This can happen if cancer metastasizes into the spinal column, says Dr. Taiwo. The cancer can press into the spinal cord and surrounding nerves (which are protected by the spinal column), causing weakness or numbness in the limbs—particularly the lower extremities, she says. If not addressed, a person can lose function of their bladder, bowels, or limbs. This is a less common complication affecting an estimated 3%–5% of cancer patients, as reported in the journal Clinical Medicine—although it's more likely to happen in patients with breast, prostate, and lung cancer.  

Hypercalcemia

This is where a person has too much calcium in their blood. It can be a complication of metastatic breast cancer (although it can happen in earlier-stage breast cancers). "Whenever there's cancer in the bone, calcium can leach out," says Dr. Montero. Cancer cells release cytokines and proteins that disrupt the bone regrowth process, making the bone break down faster than it can regenerate itself—releasing calcium into the blood. "Really high calcium levels can cause heart abnormalities," he says, as well as confusion, excessive thirst, confusion, and lethargy. Hypercalcemia is often a sign that the cancer has advanced significantly, and is associated with a poorer prognosis despite newer advancements in treatment, according to data in the Journal of Clinical Oncology.

Malignant pleural effusion

This is a complication of metastatic breast cancer in the lungs. It is caused by the buildup of cancer cells and excess fluid in the pleura (aka the tissues that cover and protect the lungs). Normally these tissues have a small amount of fluid for lubrication, says Dr. Montero, which gets reabsorbed by your lymphatic system. "When there's metastatic cancer, it can clog up the lymphatic system in your chest," he says, leading to a buildup of fluid that causes coughing, shortness of breath, and chest pain.

How is metastatic breast cancer diagnosed?

Usually an earlier-stage breast cancer diagnosis happens by mammogram, says Dr. Lin. Often there's a follow-up with an ultrasound or MRI, then biopsy, to confirm that it is breast cancer and not a benign mass. But with metastatic breast cancer, a patient usually has already been diagnosed with and treated for breast cancer. So diagnosis typically comes in response to new symptoms.  

"Our antennae are always up," says Dr. Taiwo, if a patient with a history of breast cancer starts experiencing symptoms like new bone pain or unexplained nausea or weight loss. "We have a low threshold to investigate further to see if the patient is now metastatic."

For example: If a patient who was initially diagnosed with stage 2 breast cancer later complains of hip pain and trouble walking, Dr. Lin says that she'll typically do an X-ray and a bone scan to see if there's any evidence of cancer in the bone. Similarly, if a person with a history of breast cancer starts experiencing headaches and dizziness, a doctor may perform an MRI to see whether the cancer has spread to the brain. 

In the future, Dr. Tsarwhas says there may be more proactive ways to diagnose metastatic breast cancer in the future, such as blood tests that can detect metastatic breast cancer cells in the bloodstream. Dr. Lin says that these kinds of tests could help doctors begin treatment and potentially even eradicate the cancer before it progressed to stage 4. Treatments are also improving to help drastically increase a patient's lifespan, Dr. Tsarwhas adds.

If you have a history of breast cancer and are experiencing new, troubling symptoms, be sure to talk to your doctor as soon as possible. "There are times for optimism given all of the research and developments that have happened in the treatment of breast cancer," Dr. Tsarwhas says. By being proactive about any metastatic breast cancer symptoms you have, you can help ensure that you are getting the best possible care—and improving your odds for living a longer life with the disease.

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