Localization and invasion by a soft tissue tumor induced by pellets made of hydroxypropylcellulose mixed with 20-methylcholanthrene in the femur of rats.

Abstract

Pellets made of a carcinogenic substance, methylcholanthrene, admixed with a high molecular weight substance, hydroxypropylcellulose, were implanted into the thigh of 90 rats (three groups, 30 rats each). In Group 1, the pellets were placed at the window made in the cortex of the femur; in Group 2, into the space between the dorsal femoral cortex and periosteum; and in Group 3, into the pouch created outside of the dorsal periosteum. Twenty weeks after implantation, rhabdomyosarcoma developed in 28 rats in Group 1, 27 in Group 2, and 21 in Group 3. Tumor invasions into the marrow of the femur were seen in 14 rats in Group 1 and 5 in Group 2. In Group 3, however, tumor invasion was not observed. There were significant differences in the invasion rate of tumor between Groups 1 and 2 (P < 0.01) and between Groups 2 and 3 (P < 0.05). At implant sites, Group 2 showed thinning out of the periosteum, whereas in Group 3 thickening of both cortex and periosteum was found. These experimental results are interpreted to mean that the periosteum provides an important barrier around the bone against tumor invasion into the bone.