Thymic atrophy induced by murine mammary adenocarcinoma in vivo.

The thymic compartment of mammary tumor bearing mice is severely affected with increasing tumor growth. T cell functions in peripheral organs are greatly impaired or absent in such animals. A study of the thymus in relation to tumorigenesis revealed a profound decrease in size accompanied by a disrupture of the normal thymic architecture. Although a strong splenic suppressor cell activity can be detected in this animal model, splenectomy did not prevent thymic involution. Injection of tumor associated factors into normal mice resulted in a thymic atrophy similar to that seen in tumor bearing mice. These findings indicate that the observed thymic involution may not be only due to stress-related phenomena but also a direct effect of the tumor.