Spleen weight in rats during tumour growth and in homograft rejection.

The spleens of rats bearing methylcholanthrene induced sarcomas are enlarged. This applies both to primary and to isotransplanted tumours. The spleen enlarges with increasing tumour size.Splenomegaly is induced by skin homograft rejection, but spleen sizes do not reach those seen during tumour growth, even when the animals are chronically exposed to homologous skin. Sensitization of animals with small tumour homografts gives spleen sizes even greater than those of primary tumour growth.Spleen histology in tumour bearing animals is comparable with that of homograft rejection.The relation of splenomegaly to the presence of tumour specific antigen is discussed. The suggestion is advanced that the spleen size during tumour growth is determined by the product of reaction to foreign antigen, and of reticuloendothelial (phagocytic) activity.