Learn The BasicsThere are a number of medical therapies for breast cancer. These include chemotherapy agents, hormone therapy, immunotherapy, targeted therapies and antibody-drug conjugates.
Chemotherapy and radiotherapy for breast cancer
Chemotherapy refers to the use of drugs that target and destroy cancer cells.
It is most effective when two or more chemotherapy drugs are used in combination. These drugs may be administered intravenously or orally.
Chemotherapy for breast cancer is usually used either before or after surgery. Chemotherapy given before surgery is called neoadjuvant chemotherapy and aims to reduce the size of the tumor before it can be removed. Chemotherapy that is given after surgery is called adjuvant chemotherapy and aims to get rid of any residual cancer cells that may have been left behind during surgery.
Chemotherapy may also be the first-line therapy in case of metastatic breast cancer, meaning the cancer has spread to other parts of the body.
Neoadjuvant and adjuvant chemotherapy drugs that are often used to treat breast cancer include anthracyclines, like doxorubicin (Adriamycin) and epirubicin (Ellence), taxanes, like paclitaxel (Taxol) and docetaxel (Taxotere), 5-fluorouracil (5-FU) or capecitabine (Xeloda), cyclophosphamide (Cytoxan) and carboplatin (Paraplatin).
Chemotherapy drugs used to treat metastatic breast cancer include taxanes like paclitaxel (Taxol), docetaxel (Taxotere), and albumin-bound paclitaxel (Abraxane), ixabepilone (Ixempra), eribulin (Halaven), anthracyclines like doxorubicin (Adriamycin), liposomal doxorubicin (Doxil) and epirubicin (Ellence), platinum agents like cisplatin and carboplatin, Vinorelbine (Navelbine), capecitabine (Xeloda) and gemcitabine (Gemzar).
Radiotherapy, also known as radiation, may also be used as a neoadjuvant or adjuvant therapy in breast cancer. Approaches include external beam radiation and internal radiation.
Hormone therapy for breast cancer
Hormone therapy can be effective in treating breast cancer that is hormone receptor-positive. This means that cancer cells express estrogen or progesterone receptors on their surface, which help them grow and spread.
Hormone therapy can either be used as neoadjuvant or adjuvant therapy before and after surgery or to treat metastatic or recurrent breast cancer.
There are different types of hormone therapy for breast cancer. These include therapies that block estrogen receptors like selective estrogen receptor modulators (SERMs) and selective estrogen receptor degraders (SERDs) and therapies that lower the levels of estrogen like aromatase inhibitors and luteinizing hormone-releasing hormone (LHRH) agonists.
SERMs block estrogen from binding to the estrogen receptor on the surface of cancer cells. They include tamoxifen (Nolvadex) and toremifene (Fareston).
SERDs inhibit the communication of estrogen with cancer cells by destroying the estrogen receptors on their surface. SERDs used to treat breast cancer include fulvestrant (Faslodex), elacestrant (Orserdu) and imlunestrant (Inluriyo).
Aromatase inhibitors are drugs that stop the production of estrogen in the body by inhibiting the action of an enzyme called aromatase, which is responsible for making estrogen from fat. Examples of aromatase inhibitors used to treat breast cancer include letrozole (Femara), anastrozole (Arimidex) and exemestane (Aromasin).
Finally, LHRH agonists work by inhibiting the signal from the brain that tells the ovaries to make estrogen. Examples include goserelin (Zoladex) and leuprolide (Lupron).
Immunotherapy for breast cancer
Immunotherapy works by training the body’s own immune system to recognize and destroy breast cancer cells. It is usually used to treat high-risk curable early-stage and metastatic triple-negative breast cancer. It may also be used as neoadjuvant or adjuvant therapy before or after surgery to reduce the risk of recurrence.
The main immunotherapy drugs that are used to treat breast cancer are pembrolizumab (Keytruda) and dostarlimab (Jemperli).
These are both immune checkpoint inhibitors. They work by blocking a protein called programmed cell death 1 (PD1) that is found on the surface of specialized immune cells called T- cells.
Normal healthy cells in the body express a protein called PD-L1 that binds to PD1, thereby ensuring that the T-cells do not destroy them.
Cancer cells express a very large amount of PD-L1 inhibiting T-cell activity, allowing them to evade immune destruction.
By blocking the PD-1 protein on the surface of T-cells, pembrolizumab and dostarlimab ensure that the PD-L1 protein found on the surface of the cancer cells cannot bind to it, thereby “waking up” the T-cells to recognise the cancer cells as abnormal and destroying them.
Targeted therapies for breast cancer
These therapies target proteins found on the surface of cancer cells that help them grow and spread.
There are different types of targeted therapies used to treat breast cancer. These include monoclonal antibodies, kinase inhibitors, CDK4/6 inhibitors, mTOR inhibitors, PI3K inhibitors, AKT inhibitors and PARP inhibitors.
Monoclonal antibodies are proteins resembling immune-system proteins that attach to certain proteins like HER2 found on the surface of cancer cells, marking them for destruction by the immune system. Anti-HER2 monoclonal antibodies used to treat breast cancer include trastuzumab (Herceptin), pertuzumab (Perjeta), trastuzumab, pertuzumab and hyaluronidase combination (Phesgo) and margetuximab (Margenza).
Kinase inhibitors are agents that block a protein called kinase, the role of which is to relay signals to cells, like telling them to grow. By blocking the activity of these proteins, kinase inhibitors could help shrink breast cancer. Kinase inhibitors commonly used to treat BC include Lapatinib (Tykerb), neratinib (Nerlynx) and tucatinib (Tukysa).
CDK4/6 inhibitors are agents that block a type of protein called cyclin-dependent kinases (CDKs), which are essential for cell division. CDK4/6 inhibitors used in breast cancer include palbociclib (Ibrance), ribociclib (Kisqali) and abemaciclib (Verzenio).
mTOR inhibitors block a protein called mTOR, which also helps cells grow and divide. Everolimus (Afinitor) is an mTOR inhibitor used to treat breast cancer that may also stop tumors from developing new blood vessels, thereby limiting their growth.
PI3K inhibitors also stop cell growth. Examples used to treat breast cancer include alpelisib (Piqray) and inavolisib (Itovebi).
Another protein that helps cells grow is AKT. Capivasertib (Truqap) is an AKT inhibitor used to treat breast cancer.
Finally, PARP inhibitors are specific for BRCA-mutated breast cancer. PARP and BRCA are proteins that are responsible for repairing DNA damage. Mutations in the gene that codes for BRCA proteins are what cause breast cancer in the first place in some instances. Blocking the other DNA damage repair protein results in the cells no longer being able to repair their DNA and dying. PARP inhibitors used to treat BRCA-mutated breast cancer include olaparib (Lynparza) and talazoparib (Talzenna).
Antibody-drug conjugates for breast cancer
Antibody-drug conjugates combine chemotherapy with targeted therapy. The antibody portion of the drug recognizes cancer cells and directs the chemotherapy agent to them.
The four main antibody-drug conjugates used to treat breast cancer are sacituzumab govitecan-hziy (Trodelvy), fam-trastuzumab-deruxtecan-nxki (Enhertu), T-DM1 or ado-trastuzumab emtansine (Kadcyla) and datopotamab-deruxtecan (Datroway or Dato-DXd).