Low level of cyclin D1 protein expression in thyroid microcarcinomas from an autopsy series

In a recent epidemiological screening study in an autopsy series, we found a high prevalence of microcarcinomas (MCs) (21/443 = 4.74%). We found no iodine intake-, gender-, or age-dependent differences in the prevalence of MCs. The results suggest a different and benign behavior of MCs compared to clinical cancer. The role of cyclin D1 overexpression in the pathogenesis of thyroid tumors is not known clearly; however, overexpression of this protein was reported in well-differentiated papillary cancers and in incidentally found metastasizing MCs. To date, cyclin D1 expression has not been investigated in autopsy-derived thyroid MCs. Eight MCs were available for immunostaining and comparison with 15 clinically detected papillary thyroid cancers. Fourteen out of 15 clinical carcinomas expressed cyclin D1 (93.3%), while in the MCs this ratio was 1 out of 8 (12.5%) (p = 0.0001). The only cyclin D1-positive MC was multifocal (both lobes of the gland were affected). We concluded that the benign behavior of most autopsy-derived MCs may be associated with the lack of cyclin D1 overexpression.