Targeted therapies are drugs that interfere with molecular targets—things like proteins, genes and hormones. These targets can be on the cancer cell itself or on other cells the cancer needs to help it grow and spread. The target can also be inside cells. Normal cells do not have these targets. As a result, targeted therapy is very specific to cancer cells. Lab tests are usually performed on biopsy tissue to determine if eligible targets are present, and whether or not the patient is an eligible treatment candidate. Targeted therapy is different from standard chemotherapy. Standard chemotherapy works by killing rapidly dividing cells, such as cancer cells. However, your body also has normal rapidly dividing cells, including hair follicles, bone marrow, and the lining of the digestive tract. Standard chemotherapy will also kill many of these cells. This accounts for many of the side effects and toxicities of standard chemotherapy. Targeted therapy does not harm normal cells because they lack the molecular targets it engages. Because of this, targeted therapy does not have the same side effects as standard chemotherapy. There are side effects, but they are different and people tend to tolerate them better. The side effects vary depending on the type of targeted therapy. There are two main types of targeted therapy. The two main types of targeted therapy include: Monoclonal antibodies use targets on the surface of cancer cells. When they attach to these targets, they interfere with the cancer cell’s ability to grow. They can also carry toxic substances directly to the cancer cell using these surface targets. Growth factors outside the cancer cell are other targets for monoclonal antibodies. These drug names end with –mab, for monoclonal antibody. Small molecules can go inside cells to act on a target. This includes both cancer cells and other kinds of cells that perform functions the cancer cell needs to grow and spread. Enzymes are often targets of these small molecule drugs. Interfering with or inhibiting enzymes stops various cellular functions. These drug names end with –ib, for inhibit. Immunotherapy can be a form of targeted therapy. Cancer treatment guidelines typically list immunotherapy as a separate category of cancer therapy. Malignant tumors are often able to fool the immune system and grow without detection. Immunotherapy is any therapy that boosts your own immune system to fight cancer. There are various ways to do this, including using interferons, interleukins, and cancer vaccines. Monoclonal antibody therapy—one of the targeted therapy classes—is also an immunotherapy. Your healthy immune system already uses antibodies to fight infections. Monoclonal antibodies are made in a lab to perform specific functions. Therapeutic monoclonal antibodies can target cancer cells or immune system pathways to increase your immune system’s ability to recognize and fight the cancer. Hormone therapy can be a form of targeted therapy. Like immunotherapy, cancer treatment guidelines usually list hormone therapy as a separate category. However, it can be a form of targeted therapy. Some cancers depend on hormones to grow. These cancer cells have receptors on their surface where the hormones attach. Hormone attachment triggers other events that cause cancer growth. There are two approaches to using this dependence on hormones to treat cancer. The first involves lowering hormone levels to starve the cancer. The second is a targeted therapy to block the hormone receptor. This prevents the cancer from using the hormones it needs. Targeted therapy is a treatment option for many types of cancers. Targeted therapy will not work for all cancers. Your doctor will need to run tests to find out if your cancer is likely to respond. These tests will look for molecular markers, gene mutations, and other factors. When any of these are present, targeted therapy may be an option. Some of the more common cancers that may respond to targeted therapies include: Basal cell skin cancer (the most common type) Breast cancer Cervical and ovarian cancers Colorectal cancer Leukemia, lymphoma, and other blood cancers Lung cancer Melanoma Thyroid cancer Targeted therapy is an area of tremendous growth for cancer treatment. There are a wide variety of targeted therapies on the market and many more in clinical trials. Researchers continue to identify and study useful targets for cancer treatments.