Spontaneous regression of induced parotid gland tumors in rats

Pellets of powdered DMBA were implanted in the parotid glands of inbred male Fischer rats, and all experimental animals in which the carcinogen was implanted for 8, 10, 12, and 14 weeks developed well-differentiated squamous-cell carcinomas. When the carcinogen was implanted for longer periods of time, tumors developed in a smaller percentage of the experimental animals. Also, the weight of the parotid glands continued to increase with time following implantation of DMBA, reaching its highest level after 10 weeks, and then gradually decreasing with time. Different possible explanations for the regression of the induced parotid tumors are offered.