Fetal microchimerism and cancer.

The acquisition and persistence of fetal microchimerism, small numbers of genetically disparate cells from the fetus in the mother, is now a well-recognized consequence of normal pregnancy. Fetal microchimerism has been associated with several classical autoimmune diseases, but its role in normal health remains undefined. One potential function of fetal microchimerism might be in the surveillance for malignant cells. Convergent evidence is reviewed here in cancer epidemiology and transplantation biology that suggests a new paradigm in which fetal microchimerism serves as an additional line of defense against the development of breast cancer in parous women.