Bacteria, viruses and other illness-causing invaders carry proteins called antigens. When they enter your body, your immune system tries to protect you by producing antibodies — other proteins that latch onto the antigens and alert the rest of the immune system to destroy them.

How monoclonal antibodies work

Different types of cancer produce different types of antigens. A monoclonal antibody is a man-made antibody designed to zero in on the specific antigens associated with a certain type of cancer. Once the monoclonal antibody attaches to the specific antigen on the cell, it alerts the immune system to come destroy it or blocks signal from the cell that help it grow. Different monoclonal antibodies work in different ways: They can kill cancer cells, cut off blood supply to the tumor, carry chemotherapy drugs straight to the cancer cells, block proteins that enable cancer cells to grow, and “show” the immune system where cancer cells are hiding.

For example, the cancer drug Herceptin (trastuzumab) is a monoclonal antibody that seeks and finds breast or stomach cancer cells that have higher levels of the antigen called HER2. The trastuzumab antibody attaches to these cells and blocks a signal within the cell that tells it to grow and multiply and the cancer cells stop growing. The trastuzumab antibody also recruits other immune cells to kill the cells with HER2.

Because the antigens on the cancer cells are not produced by healthy cells (or in much lower amounts), only the cancer cells are targeted by this treatment. The FDA has approved several monoclonal antibodies to treat cancers such as lymphoma, head & neck, ovarian, leukemia and breast, and many more are being developed every day.

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