Fetal cell microchimerism in papillary thyroid cancer: studies in peripheral blood and tissues.

Fetal cell microchimerism (FCM) is defined as the persistence, for decades after pregnancy, of fetal cells in maternal organs and circulation without any apparent rejection. We recently reported evidence, in papillary thyroid cancer (PTC) tissues, supporting a possible role of FCM in tumor damage and repair. To extend those data at the peripheral level, 106 women with a previous male pregnancy, comprising 57 with PTC and 49 healthy controls were enrolled. The presence of circulating male DNA was assessed by the amplification of the Y chromosome-specific gene SRY, with a sensitivity of 1 male cell per 1 million female cells. Moreover, to compare the microchimeric status in blood and in tumors, the neoplastic tissues of 19 women were studied. At the blood level, a significantly lower frequency of FCM was found in parous women with PTC with respect to controls (49.1% vs. 77.6%; p = 0.002). By PCR, male DNA was identified in the tumor tissues of 6 patients, and FISH analyses confirmed the presence of microchimeric cells (range 2.1-6.9 cells/section). In some patients, FCM was negative in the blood, whereas microchimeric cells were identified in the tumor. In conclusion, the prevalence of FCM in peripheral blood was found to be significantly lower in patients than in healthy controls. The presence of microchimeric cells in the tumors, but not at the peripheral level, supports the hypothesis that fetal cells could reside in maternal niches and could be recruited to diseased areas, where they could differentiate to regenerate damaged tissues.