Plasma thyroid-stimulating hormone and thyroxine concentrations in breast cancer.

Plasma TSH and thyroxine levels were measured in 74 early breast cancer patients and 53 with advanced disease, 77 patients with cancer arising in other organs and 67 healthy women of similar age. The mean plasma TSH levels were higher in the breast cancer cases than the other two groups; the difference was statistically significant only in those with advanced disease. Twelve percent of the early breast cancer and 15% of the advanced breast cancer patients had elevated plasma TSH concentrations, compared with only 1% of the other cancer patients and 3% of the controls. Four breast cancer patients with plasma TSH levels above 85 microIU/ml had subnormal plasma thyroxine levels. Five of 29 (17%) early breast cancer patients had excessive plasma TSH responses to TRH.