We studied the effect of
thyroxine treatment on
tumor growth and
metastases resulting from
tumor implants on the hind feet of mice in two syngeneic systems. In control, untreated A/Jax mice,
tumor Sarcoma 1 at Day 14 after implantation had average
tumor weight of 582 +/- 60 (S.D.) mg and showed an incidence of 57%
metastases to regional popliteal nodes and 5%
metastases to thymus. In contrast, the
thyroxine-treated group (40 microgram/mouse s.c., 5 times/week for 1 month) had an average
tumor weight of 808 +/- 56 mg (p less than 0.001), and
metastases to popliteal nodes and thymus were 90 and 35%, respectively. In another syngeneic
tumor system, Lewis
fibrosarcoma was implanted in C57BL/6J mice, and the
tumor weight and metastatic index (derived from the number and size of the pulmonary
tumor foci) were determined at Day 28. Again, the synthetic
L-thyroxine treated group showed a significant enhancement
tumor growth and metastatic index. The mean
tumor weight in the treated group was 385 +/- 26 mg (control, 694 +/- 25 mg; p less than 0.005) and metastatic index was 84 +/- 29 (control, 30 +/- 25; p less than 0.001). Induced
hypothyroidism (treatment with 131I, 100 microCi/mouse i.p.) showed the reverse effect on both
tumor systems. These results suggest that both
tumor systems are dependent on
thyroid hormones for their growth and spread.