by Mona Jhaveri - November 24, 2021

Breast cancer is the most common type of cancer diagnosed in women – it affects one out of every eight women in the United States.

Established treatments for breast cancer range from surgery and chemotherapy to radiation and hormone therapy, while breakthrough treatments consist of targeted therapy and immunotherapy.

In this blog post, we will discuss both the current and breakthrough treatments of breast cancer.

Breast Cancer Subtypes

Breast cancer is not only one disease. It comes in subtypes, all of which respond differently to treatments.

The three primary clinical subtypes of breast cancer are:

  • Hormone-receptor-positive breast cancer – The most common subtype, HR-positive cancer, occurs when the cells of breast tumors have receptors for estrogen and/or progesterone.
  • Human epidermal growth factor receptor-2 positive breast cancer – Also known as HER2-positive breast cancer, it occurs when receptors for a growth factor called human epidermal growth factor receptor 2 (HER2) are expressed in tumors. They can be HR-positive or HR-negative.
  • Triple-negative breast cancer – Also called TNBC, triple-negative breast cancer occurs when tumors are negative for the estrogen receptor (ER), progesterone receptors (PR), and HER2.

Surgery

According to the American Cancer Society, most women diagnosed with breast cancer undergo some type of surgery to treat the cancer.

There are two main surgery types for this cancer:

  • Breast-conserving surgery (BSC, lumpectomy, quadrantectomy, partial mastectomy, or segmental mastectomy) – involves removing the tumor and some surrounding healthy tissue while sparing as much breast tissue as possible.
  • Mastectomy – involves surgically removing all of one or both breasts to treat cancer that has spread beyond the original site. Mastectomies are usually performed in conjunction with additional surgical procedures such as breast reconstruction.

Surgery may also include sentinel lymph node biopsy (SLNB) or axillary lymph node dissection (ALND) – to find and remove the lymph nodes that contain cancer cells.

In sentinel lymph node biopsy, only one or a few of the closest lymph nodes are removed and checked for cancer cells. In axillary lymph node dissection, more than two lymph nodes (usually fewer than 20) are removed and checked for cancer cells.

All of these procedures may be followed by radiation therapy or chemotherapy, depending on the stage of breast cancer.

Radiation Therapy

Another local type of breast cancer treatment, radiation therapy, uses high-energy x-rays or other types of radiation to kill cancer cells. This therapy is used for people with early-stage breast cancer that has not spread far beyond the original site. Radiation may be given before surgery, after surgery, or both.

Two main types of radiation can be used to treat breast cancer:

  • External beam radiation – A machine delivers high-energy rays from outside the body to kill cancer cells. Parts of the body that will be exposed to radiation depend on the location of the tumor. They could include the whole breast, a part of the breast, the entire chest wall, with or without lymph nodes under the arm, above the collarbone, or behind the breast bone.
  • Brachytherapy – Also called internal radiation, brachytherapy uses small amounts of radioactive material sealed in needles, pellets, wires, or catheters that are inserted directly into the tumor.

Chemotherapy

Chemotherapy, or chemo for short, represents the use of anti-cancer drugs to treat cancer. The goal of chemotherapy is to stop or slow cancer growth and the spread of breast cancer cells.

Two main types of chemo for breast cancer are:

  • Adjuvant therapy – This treatment is given to breast cancer patients who have been treated with surgery. This type of treatment aims to kill any remaining cancer cells to prevent them from growing into more serious tumors later on.
  • Chemotherapy to treat metastatic breast cancer (advanced breast cancer) – This treatment is given when the tumor has spread, and it’s too late to use surgery or radiation therapy.

Chemotherapy can be taken by pill, injection, or infusion through a tube placed in the vein (IV). The most common chemo drugs used in the treatment of breast cancer are:

  • Doxorubicin (Adriamycin)
  • Cyclophosphamide (Endoxan, Neosar)
  • Epirubicin (Ellence)
  • Fluorouracil (Carac, Efudex)
  • Paclitaxel (Taxol)
  • Docetaxel (Taxotere)
  • Carboplatin (Paraplatin)
  • Cisplatin (Platinol, Platinol AQ)

Hormone Therapy

About 2 out of 3 breast cancers that are discovered belong in the hormone-receptor-positive group. These tumors have growth-promoting proteins called receptors that are affected by hormones such as estrogen or progesterone.

Treatment with hormonal therapy is used for women who have tumor cells containing these receptors. The drugs used in hormone therapy block the body’s estrogen, progesterone, and other hormones to slow the development of cancer cells that feed off of these hormones.

Hormone therapy drugs can be divided into two categories:

  • Drugs that block estrogen receptors – Tamoxifen, Toremifene, Fulvestrant
  • Drugs that lower estrogen levels in the body – Aromatase inhibitors (AIs), such as Letrozole, Anastrozole, Exemestane

In conjunction with hormone therapy, one more option is ovarian suppression, which uses certain drugs that shut down or otherwise reduce estrogen production in premenopausal women.

Targeted Therapy

Targeted therapy is a type of treatment that uses special types of drugs that identify and attack cancer cells without harming normal tissues. This is in contrast to chemotherapy that doesn’t entirely differentiate between healthy cells and cancer cells.  Consequently, chemotherapy can cause a lot of damage to normal functions of the body during treatment.

Targeted therapy is given when the tumor has spread beyond the breast, but it can be used in addition with other forms of treatments for local disease or invasive breast cancer.

Targeted therapy drugs can be used for the treatment of all three major breast cancer subtypes:

  • HR-positive – CDK4/6 inhibitors (palbociclib, ribociclib, ademaciclib), mTOR inhibitor (everolimus), PI3K inhibitor (alpelisib – approved by the FDA in May 2019)
  • HER2-positive – monoclonal antibodies (trastuzumab, pertuzumab, margetuximab), antibody-drug conjugates (ado-trastuzumab emtansine, fam-trastuzumab deruxtecan – approved by the FDA in December 2019)
  • Triple-negative – antibody-drug conjugate (sacituzumab govitecan – approved by the FDA in April 2020 for treatment of metastatic triple-negative breast cancers that haven’t responded to at least two other types of treatments)

Immunotherapy

Immunotherapy drugs work by restoring normal immune functions that have been disabled by cancer cells. 

Immune checkpoint inhibitors are a type of immunotherapy that targets specific proteins (“checkpoints”) on the surface of T cells. In normal function, when a checkpoint inhibitor binds to the checkpoint, it helps T cells attack cancer cells by allowing them to recognize the cancer cells more efficiently.

Currently, one immune checkpoint inhibitor (pembrolizumab) is approved to treat breast cancer, more specifically for the treatment of early-stage triple-negative breast cancer that has a high probability of returning. 

Pembrolizumab works by blocking PD-1 receptors on lymphocytes (immune system cells). This receptor is the main reason why the immune system cannot attack cancer cells. Certain types of cancer, including breast cancer, produce special PD-L1 proteins that bind to the PD-1 receptors and prevent the body’s immune system from killing cancer cells. Pembrolizumab is in charge of blocking the PD-1 receptors, allowing the immune system to target and destroy cancer cells.

This drug was approved by the FDA as recently as July 2021.

Conclusion

Well-established treatment options for breast cancer include surgery, radiation, chemotherapy drugs, and hormone therapy. Breakthrough therapies consist of new targeted and immunotherapy medicines that aim to slow cancer cell growth or eradicate them without harming surrounding healthy cells.

The science and medical world still have a long way to go as new cancer research is published every day on the subject. Treatments for breast cancer are constantly changing, but researchers continue to make progress in their search for a cure while also improving patient care along the way.

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