The incidence of breast tumor during experimental hyperthyroidism.

The incidence of breast tumor in inbred C3H-A mice (virgin female) from hyperthyroid, hypothyroid, and euthyroid control groups at week 44 of the experiment was 86.67, 30, and 62.5%, respectively. The percentage of metastatic lymph nodes in these groups was 65.9±16.7, 35.9±5.9, and 53.9±7.2%, respectively (p<0.005). It was shown that hyperthyroidism was associated with increased incidence and aggressiveness of breast tumor, while hypothyroidism was associated with lower incidence of breast tumor in comparison with the control.