Thyroid function in early breast cancer.

Serum 'free thyroxine' was measured as a thyroid function index (TFI) in 238 women with early breast cancer and 107 normal controls. The mean TFI was significantly lower in the cases compared with controls. The TFI was not related to pathological stage but correlated with histological grade, with the highest values found in well-differentiated (grade I) and the lowest in anaplastic tumours (grade III). A similar result was obtained with the urinary and androsterone:aetiocholanolone (5 alpha:5 beta) ratio in that the ratio was significantly lower in patients with grade III than in those with grade I tumours. These results indicate that thyroid hormones may be involved in tumour cell differentiation. Patients with low 5 alpha/5 beta ratios had significantly faster recurrence rates than those with high ratios. A similar trend was found for the TFI. The TFI decreases after mastectomy and at 12 months after operation is still below the pre-operative basal level.