Fetal cell microchimerism in papillary thyroid cancer: A role in the outcome of the disease.

Fetal cell microchimerism (FCM) is defined as the persistence of fetal cells in maternal organs and circulation without any apparent rejection and it was hypothesized to protect toward the onset of some neoplastic diseases. To verify the role of FCM in papillary thyroid cancer (PTC), we enrolled 87 parous women with PTC and at least one male pregnancy preceding the diagnosis (PTC-P), 66 healthy women with 1 or more male children (HC-P) and 57 nonparous women with PTC (PTC-NP). 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/1 million female cells. A significantly higher frequency of FCM was found in HC-P than PTC-P women (63.6% vs. 39.1%, p = 0.004). Among PTC-P patients, those positive for the presence of FCM (FMC+ve) had a lower prevalence of extrathyroidal extension (p = 0.027) and lymph node metastases (p = 0.044) than those without FCM (FMC-ve). Moreover, FMC+ve patients were more frequently in remission than FMC-ve cases (94.1 vs. 67.9%, p = 0.009). Interestingly, we showed for the first time that the positive effect on tumor presentation and outcome is specifically related to FCM and it is not an effect of pregnancy. In conclusion, circulating FCM is significantly more frequent in healthy parous women than in women with PTC. Moreover, the presence of circulating fetal male cells is associated with a significantly lower extrathyroidal extension and a good prognosis, suggesting a protective role of this phenomenon toward both the onset and the progression of thyroid cancer.