glands. Increased incidence of SS after childbirth suggests a relationship between SS and pregnancy, and this led to hypothesis that fetal microchimerism may be involved in SS pathogenesis. Studies showed presence of the Y-chromosome-positive fetal cells in minor salivary glands in 11 of 20 women with SS but in only one of eight normal controls. Fetal cells in salivary glands suggest that they may be involved in the development of SS. Oral lichen planus Lichen planus (LP) is a T-cell-mediated autoimmune chronic disease of unknown etiology. Females have a three times higher prevalence than men. LP is characterized by T lymphocytes infiltration of the lower levels of epithelium, where they damage basal cells and cause apoptosis. The fetal microchimerism may trigger a fetus versus host reaction and therefore may play a role in the pathogenesis of autoimmune diseases including LP. Breast cancer Pregnancy has a positive effect on the prognosis of breast cancer according to several studies also it apparently increases the chance of survival after diagnosis of this tumor disease. Possible positive effects of pregnancy could be explained by the persistence of fetal cells in the blood and maternal tissues. Fetal cells are probably actively migrating from peripheral blood into the tumor tissue where they are preferentially settled in the tumor stroma and their concentration decreases as they get closer to the healthy breast tissue. There are two suggested mechanisms by which the fetal cells could have the positive effect on the breast cancer prognosis. First mechanism suggests that fetal cells only oversee cancer cells and they attract components of the immune system if needed. The second option is that the down-regulation of the immune system induced by the presence of fetal cells could ultimately lead to cancer prevention, because women in whom FMC is present produce lower concentrations of inflammatory mediators, which may lead to the development of neoplastic tissue. The effect also depends on the level of microchimerism: Hyperchimerism (too high a degree of microchimerism) can, as well as hypochimerism (low rate of microchimerism), be related to the negative effect of FMC and thus can promote worse prognosis of breast cancer. Apparently, women with breast cancer may fail in the process of obtaining and maintaining allogeneic fetal cells. Low concentration and / or complete absence of fetal cells could indicate a predisposition to development of the malignant process. Other cancers Study of S. Hallum shows association between