Plasma thyronine levels in carcinoma of the breast and colon

Plasma triiodothyronine (T3), reverse T3 (rT3), thyroxine (T4), total thyroid hormone-binding globulin (TBG) capacity, and serum albumin were assayed in patients with early and advanced breast and colonic cancer and in healthy women. Plasma T3 levels were reduced in both breast cancer group, but were reduced only in colonic cancer patients with systemic metastases. Plasma rT3 was normal in early cancer, but increased in nine of 38 (24%) with advanced breast cancer and four of 17 (24%) with metastatic colonic cancer; in consequence their rT3/T3 ratios were elevated. Plasma T4 concentrations were normal in all patient groups. Plasma TBG capacity was reduced in breast cancer patients with systemic metastases and a similar tendency occurred in metastatic colonic cancer. Levels of TBG were positively correlated with the serum albumin values. These changes were associated particularly with liver metastases.