Effect of 3-Methylcholantren treatment on soft tissue tumor induction in Spalax and mice. Animals treated with a single injection of 3MCA as described in the Materials and methods section. Representative images show macroscopic and microscopic observations. Mice (A): An ill-defined, soft mass, with foci of necrosis and hemorrhage; diagnosed as high-grade fibrosarcoma by histology. Spalax (B): a well-circumscribed, firm, whitish nodule composed of benign spindle cells organized into long regular bundles - benign reactive fibrosis. Hematoxylin and eosin staining, ×100. 3MCA, 3-Methylcholantrene.