The Best Defense against Breast Cancer Is Pregnancy Study Shows

“When it comes to breast cancer, the best defense is an effective attack,” say researchers at Cold Spring Harbor Laboratory (New York). The study, conducted in mice and published in Cell Reports, shows how, after pregnancy (or gestation), breast cells turn to specialized immune cells, Natural Killer T cells (or NKT lymphocytes), to prevent tumor formation. These initial findings still need to be validated in women, especially late in pregnancy.



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Our immune system is constantly monitoring our body to keep it healthy. And in some cases, immune cells need to react quickly to solve a problem or respond to a threat. These scientists are exploring how pregnancy reduces the risk of breast cancer. “After pregnancy, there is an increase in NKT cells and only in the mammary gland. This expansion is not seen anywhere else in the body, although NKT cells are found everywhere else in the body,” says one of the authors, researcher Amritha Varshini Hanasoge Somasundara.

On the relationship between pregnancy and breast cancer prevention the immune system has two lines of defense:

  • The first is the innate response, which involves immune cells that attack any foreign body they encounter.
  • The second is the adaptive response, which is carried out by immune cells that respond specifically to certain calls with certain molecules.

NB: The NKT cells, a unique group of cells found throughout the body, can participate in both responses.

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In the study, the team investigated what this large number of NKT cells, which accumulate in breast tissue, does after pregnancy. The study which was conducted on mice shows that:

  • Breast epithelial cells, which line the milk ducts, produce a specific protein called CD1d after pregnancy.
  • When the cells lack this CD1d protein, there is no increase in the number of NKT cells in the breast tissue, so the epithelial cells can become cancerous and form tumors.
  • CD1d molecules thus use the NKT cells to monitor the epithelial cells in the breast tissue after pregnancy. And if the epithelial cells become cancerous, the NKT cells quickly eliminate them to prevent tumor growth.

These findings document a link between pregnancy and the immune system in preventing breast cancer. The next steps will be to validate these findings in humans, particularly in late pregnancy, and to try to translate these findings into ways to prevent breast cancer, in particular by figuring out how to induce an abundance of NKT cells in breast tissue as the women age and go through menopause.

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Parity-induced changes to mammary epithelial cells control NKT cell expansion and mammary oncogenesis



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