Metastatic breast cancer (MBC) refers to breast cancer that has spread beyond the breasts and nearby lymph nodes to other organs in the body. MBC is also known as advanced or stage 4 cancer.

MBC can develop after an initial diagnosis of earlier stage breast cancer. It is also possible for MBC to be a person’s first diagnosis.

There is currently no cure for MBC, but there are many treatment options available that can slow the cancer’s growth.

This article explores the role that genes play in the development of MBC and how genetic testing is leading researchers to newer targeted treatments.

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Mutations in genes can affect a person’s susceptibility to breast cancer. Specifically, two categories of mutations — germline mutations and somatic mutations — may increase an individual’s risk of developing breast cancer.

Germline mutations are present in every cell of the body. These mutations run in families, and a person may inherit them from a biological parent. About 5–10% of breast cancer cases develop because a person has a hereditary predisposition to the disease.

On the other hand, somatic mutations are changes that develop after birth. These changes occur in a single cell and in any cells that derive from that single cell if it divides. A person cannot inherit somatic mutations.

Some specific germline and somatic gene mutations may increase a person’s risk of developing breast cancer that progresses to MBC. For example, several germline mutations, such asBRCA1 and BRCA2, can increase the risk of breast cancer.

Genetic testing does not yet play a role in diagnosing or detecting MBC.

A doctor diagnoses MBC the same way they do other stages of breast cancer — with laboratory tests, imaging tests, and biopsies.

However, research is ongoing into how genetic testing can help oncologists, who are doctors specializing in cancer, detect breast cancer just as it starts to spread beyond the affected breast.

If a person already has a metastatic breast cancer diagnosis, a doctor may recommend genetic testing to help determine the most suitable treatment plan.

Genetic testing is useful for determining a person’s risk of developing breast cancer.

The National Comprehensive Cancer Network indicates genetic testing when a person:

  • has a blood relative with a variant in an implicated gene known or likely to cause breast cancer
  • has a personal history of breast cancer and meets other subcriteria, including age and previous cancer diagnosis
  • has a first- or second-degree blood relative who meets any of the criteria above

The results of genetic testing can be valuable to family members as well.

Standard treatments for MBC are drug therapies such as:

  • chemotherapy
  • immunotherapy
  • hormone therapy
  • targeted drugs

Sometimes, doctors use a combination of these therapies. In other situations, a person may need to undergo radiation therapy or surgery for palliative care, though these are uncommon for MBC.

The results of genetic testing can influence treatment plans for MBC. Certain mutations make a person eligible to receive particular therapies. The detection of genetic mutations can help doctors design more tailored and effective treatment plans.

For example, tumors due to germline BRCA mutations may respond to poly(ADP-ribose) polymerase inhibitors.

Targeted therapy may be suitable for some somatic mutations. For instance, a medication called alpelisib may be suitable for tumors due to PIK3CA mutations.

Orsedu (elacestrant) is a type of selective estrogen receptor degrader that may be suitable for people with an ESR1 mutation.

Genetic testing results can also qualify individuals for clinical trials in which they can access newer treatment options that they would not typically have access to in traditional clinical settings.

Here are answers to common questions about breast cancer.

Who is at high risk for metastatic breast cancer?

A person with human epidermal growth factor receptor 2-positive breast cancer may be more at risk of metastatic breast cancer that spreads to the liver, lungs, and brain. However, not every case of breast cancer will develop into metastatic breast cancer or stage 4 cancer. A person’s doctor can provide them with more information about their outlook.

What type of breast cancer is hereditary?

Mutations in the genes BRCA1 and BRCA2 most commonly cause hereditary breast cancer. The American Cancer Society states that around 5–10% of breast cancer cases are hereditary.

What causes breast cancer to metastasize?

Metastatic breast cancer occurs when breast cancer progresses to stage 4. This means that the cancer has spread from the primary tumor to other parts of the body. This may happen if treatment is ineffective or if a person does not receive an early diagnosis.

Certain genes may make a person more susceptible to developing metastatic breast cancer (MBC). These include two categories of genes in particular: germline mutations and somatic mutations.

Currently, genetic testing is not part of diagnosing metastatic breast cancer. However, if a person has received a diagnosis, genetic tests may help determine the best treatment options.

Breast cancer can be hereditary. If a person has concerns about their risk of breast cancer or MBC, it is best to contact a doctor for advice.