Editor's note: October is Breast Cancer Awareness Month.

Treatment for breast cancer can come in many forms. In addition to surgery to remove cancerous tissue and radiation therapy, breast cancer also is commonly treated with drugs that are taken orally or intravenously, as an infusion into a vein.

Drugs that treat cancer also are called systemic therapies. Types of systemic therapies for breast cancer include chemotherapy, hormone therapy, targeted-drug therapy and immunotherapy.

"The goal of systemic therapy is to either inhibit the growth of cancer cells or to eradicate them from the body," says Matthew Goetz, M.D., a Mayo Clinic medical oncologist. Dr. Goetz is also deputy director, translational research for the Mayo Clinic Comprehensive Cancer Center and principal investigator of the Mayo Clinic Breast Cancer SPORE.

Here's an overview of the four types of systemic therapy for breast cancer:

Chemotherapy

"The breast cancer drug treatment we think about most commonly is chemotherapy, a medication that's usually delivered by vein," says Dr. Goetz. "Depending on the type of cancer and the situation, chemotherapy can be very effective at either eradicating or substantially reducing the total volume of cancer cells in the body."

Chemotherapy and drug treatments also are effective at killing cancer cells that are not yet active, which can help reduce the chance of recurrence.

"When a woman is first diagnosed with breast cancer and she does not have any obvious evidence for cancer that has spread throughout the body, there is a chance that there may be cancer cells that are undetected," says Dr. Goetz.

Chemotherapy is used often in combination with other treatments, such as surgery, radiation or hormone therapy. Before or after surgery, your healthcare provider might recommend chemotherapy to shrink an existing tumor, or destroy remaining or undetected cancer cells throughout the body. This type of treatment is called adjuvant chemotherapy.

Chemotherapy can have some unpleasant side effects, such as nausea, vomiting, hair loss and loss of appetite. These side effects often can be prevented and improved after treatment ends, but it's important to discuss these with your healthcare provider and weigh the options of different drug treatments for your cancer diagnosis.

"There may be some women who are not candidates for these medications. We certainly encounter that," says Dr. Goetz. "The good news is that we have a variety of medications, and if a woman is unable to tolerate one medication, we can try another. We know that one drug does not fit all, so having a number of different options is very important for our patients."

Hormone therapy

Some types of breast cancer are fueled by natural hormones, such as estrogen or progesterone. Your health care provider can order tests to determine if this is the case for your cancer type. If it is, hormone therapy might be recommended.

"The most common type of breast cancer, which accounts for about 70% of breast cancers, is the estrogen-receptor-positive, or hormone-receptor-positive, type of breast cancer," says Dr. Goetz. "With this type of cancer, we know that cancer cells respond to estrogen or hormones, using them to grow or proliferate. When we use hormonal therapy, we're using drugs to either block, remove or substantially downregulate the estrogen receptor."

Because of the high prevalence of hormone-sensitive breast cancer, clinical trials have been conducted to determine if hormone therapy can be used as a prevention method for women who are at high risk for breast cancer. "These medications have been used in patients that are at high risk for developing breast cancer, and they are quite effective in that setting," says Dr. Goetz.

Targeted-drug therapy

Like chemotherapy, targeted-drug therapy works throughout the body, and it is especially effective in cancers that have spread. But targeted-drug therapy differs from chemotherapy in how it kills cancer cells. Targeted-drug therapies focus on the abnormalities of cancer cells, particularly proteins, that allow them to survive and replicate, according to the National Cancer Institute.

Proteins such as the human epidermal growth factor receptor 2, also known as HER2, promote the growth of cancer cells. When patients have cancer that is HER2 positive, cancerous tumors can be more aggressive. "HER2 is present in about 20% of breast cancers," says Dr. Goetz.

"HER2-positive breast cancer was once feared by patients. When I first started my training at Mayo Clinic, we had patients who had HER2-positive breast cancer that was incurable," says Dr. Goetz. "Over the past 20 years, there have been multiple new drugs developed that have reduced the risk for HER2-positive breast cancer by 70% to 80%. Now it is something where we say 'Well, this is a good thing because we have very active drugs that can work.'"

Identifying the abnormalities of cancer cells can help your healthcare professional determine what targeted drugs are most effective for your cancer type.

Immunotherapy

While the immune system is trained to fight off perceived threats, cancer cells can manipulate the immune system by turning off the mechanism that triggers a fight response, allowing cancer cells to replicate. Immunotherapy is a newer targeted-drug therapy that teaches your immune system to identify and kill cancer cells.

Currently, immunotherapy is approved for patients with locally advanced triple-negative breast cancer. Triple-negative breast cancer, also known as basal-like breast cancer, is not sensitive to hormones or the HER2 protein.

"When a woman has a diagnosis of triple-negative breast cancer, traditionally we've used chemotherapy. But one of the real success stories in triple-negative breast cancer treatment is immunotherapy," says Dr. Goetz.

Triple-negative breast cancer is more likely to affect people according to race. "This type of breast cancer is seen at much higher rates in African American women than in Caucasian women," says Dr. Goetz. "It's an area of intense research focus right now."

Cancer experts at Mayo Clinic continue to explore how immunotherapy and other drugs — new and existing — can fight breast cancer in different populations.

"We need to be able to individualize treatment," says Dr. Goetz.  "As Dr. Richard Weinshilboum, one of my mentors, says: 'It's about the right drug, at the right dose, for the right patient.' That's what we need to focus on."

This article originally was published on the Mayo Clinic Comprehensive Cancer Center blog.

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