Fetal cell microchimerism in papillary thyroid cancer : a possibile role in tumor demage and tissue repair

Fetal cells enter the maternal circulation during pregnancy and can persist in the maternal blood or tissues for decades, creating a physiological microchimerism. Since papillary thyroid cancer (PTC) is more frequent in female gender and it is the second more frequent tumor during pregnancy, the role of persisting microchimeric cells has been investigated. Tumour tissue specimens were obtained from 62 women with PTC, 41 of whom had at least one male child before the diagnosis of PTC. Male cells were identified by PCR ELISA studies on a male specific gene, the sex-determining region Y (SRY) and were further characterized by FISH. Male DNA was detected in the pathological tissue of the 17% of women who had a male pregnancy before the diagnosis. By FISH analyses, the total number of microchimeric male cells was significantly higher in neoplastic tissues than in normal sections. By immunoFISH, a technique combining FISH and immunohystochemistry in the same section, male cells expressing thyroglobulin were found in tumor and normal tissues, while male microchimeric cells stained with the CD45 common leukocyte antigen were detected only in pathological sections. Microchimeric cells negative for both markers were detected in tumour and in normal tissues, but they were significantly more frequent in tumoral samples. In conclusion, the present study shows for the first time the presence of fetal cell microchimerism in women affected with PTC. CD45+ male cells found in the neoplastic tissues might be committed to destroy the tumoral cells, while Tg+ cells could have a repair function. Finally, microchimeric cells negative either for CD45 and for Tg could have staminal properties able to transdifferentiate in different cellular types. The whole of the results obtained suggests a protective role of microchimerism in thyroid cancer, though a possible role in carcinogenesis of persistent microchimeric cells cannot be excluded.