Why Doesn’t the Immune System Stop Breast Cancer?

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Your immune system is designed to recognize and destroy (or at least keep in check) any foreign material that could cause you harm. It would seem like cancer cells are the ultimate foreign materials. If you were diagnosed with breast cancer, you may want to understand why your immune system didn’t stop the cancer. You might even wonder if your immune system is weak.

But getting breast cancer doesn’t mean your immune system is weak. Rather, there are two important factors that help cancer cells avoid the immune response:

  • A breast cancer cell starts out as a normal, healthy cell. A cancerous growth is a collection of cells that were once normal and healthy. Precancerous and even early breast cancer cells don’t look that much different from normal cells. They don’t shout “non-self” in the way that bacteria, viruses, and other foreign materials do — which makes things more challenging for the immune system. However, as cells transform into cancer, they do shed proteins that the immune system can recognize as antigens. Immune cells such as T cells and natural killer cells (NK cells) often respond and shut the process down before a true cancer can develop.
  • During the cancer development process, the cancerous cells develop the ability to avoid the immune system. Breast cancer doesn’t happen overnight; it develops over a period of time. As healthy cells follow the pathway toward becoming full-blown cancer cells, they are constantly mutating (or changing) their genetic information. Some of these mutations enable them to avoid detection by the immune system. Others allow cancer cells to speed up their growth rate and multiply much more quickly than normal cells do. This process overwhelms the immune system and allows the breast cancer to grow unchecked.

For breast cancer and other types of cancer, researchers are working to develop treatments that can use the immune response to help the body to better recognize and target cancer cells. These treatments are called immunotherapy or biologic therapy. You can learn more in Using the Immune Response to Treat Breast Cancer.



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