Writing about their findings in Cancer Research, a journal of the American Association for Cancer Research, the researchers have revealed that the phenomenon whereby cells from a growing foetus take up long-term residence within its mother is called foetal microchimerism.
While foetal microchimerism has been implicated as a mechanism of autoimmune disease, the researchers say that it may also benefit mothers by putting the immune system on alert for malignant cells to destroy.
During the study, the researchers recruited 82 women, 35 of whom had been diagnosed with breast cancer. Approximately two-thirds of the study subjects had had children, and more than half of them had given birth to at least one son.
Upon testing the women's blood samples, the researchers found that among the women with breast cancer, only five had male DNA in their bloodstream. Three of them previously gave birth to sons, one had had an abortion, and the other had never been knowingly pregnant.
The researchers said that in all, about 14 per cent of all women in the breast cancer group had male DNA in their bloodstream, compared to 43 per cent of women in the non-breast cancer group.
"Our research found that these persisting foetal cells may be giving a woman an edge against developing breast cancer," said lead author Dr. Vijayakrishna K. Gadi, assistant professor at the University of Washington and research associate at the Fred Hutchinson Cancer Research Center.
"This experiment of nature is all the more fascinating because for years doctors treated a number of different cancers by transplanting cells from one person to another," the researcher added.
Dr. Gadi also revealed that miscarriage and abortion, blood transfusion and a male twin that was reabsorbed into the womb at an early stage of the pregnancy could be the other reasons for the presence of male DNA in a woman's peripheral blood.
The researcher believes that the findings may provide a starting point for future research on the role of foetal microchimerism in the prevention of cancer.