An increase in host specificity of a transplantable spindle-cell tumor in mice.

eyed brown nonagouti) inbred strain of this labo ratory and because it is typically made up of spindle-shaped cells with large vesicular nuclei. The individual cells vary greatly in size in sections and interlace with one another at various angles. The histopathology of this tumor has been dis cussed (1), and for reasons presented there the descriptive term spindle-cell tumor is used. The tumor has been transplanted subcutaneously in mice of the pBr strain at 5-8 weeks of age, with very uniform results. All the present trans plants were made by the author, routinely. The tumor tissue is relatively soft and may fragment while being passed through the trocar. Beginning with the 36th transplant generation (T3«), weights of the tumor were taken at 14 days. By this time the tumor typically forms an elon gated hollow mass, and the center is generally filled with blood and tissue debris. Many of the tumors present a segmented or beaded appearance, possibly from fragmentation of the tumor. Weights do not include fluid or tissue debris; in pBr mice the tumors at 14 days average between 0.8 and 1.0 gm., quite consistently. No regressions of tumors have appeared in mice of the pBr strain. Also beginning at the T36 generation, trans plants were made into mice of the N strain, one of the three strains in the ancestry of the pBr strain. Surprisingly, the tumor grew, though much more slowly than in pBr mice (Chart 1). It has been