Anaplastic thyroid carcinomas are relatively rare and have a poor prognosis. In most cases, radical surgical procedures are impossible. Recently, a combination therapy of surgical resection, percutaneous irradiation, and chemotherapy has been described in the literature. After xenotransplantation in athymic nude mice, anaplastic thyroid carcinomas show the same histological features compared to the donors. By passing the tumor over several generations of nude mice, a constant growth rate has been observed. The model allows testing of therapeutic approaches in thyroid carcinoma tissues under in vivo conditions. In 2 different studies with 2 different anaplastic transplants, a statistically significant growth inhibition could be observed using doxorubicin therapy. In one study, combination therapy was performed. The results show no statistically significant difference in the group treated by doxorubicin alone. Further investigations, under in vivo conditions, will show whether a suitable combination therapy for anaplastic thyroid carcinoma can be developed.In most series, anaplastic thyroid carcinomas make up 5-30% of thyroid malignancies [1]. In central Europe over the last few years, there has been a slight decrease in anaplastic carcinomas and an increase of well-differentiated tumor [2]. In our own material, anaplastic thyroid carcinomas were found Supported by Deutsche Forschungsgemeinschaft, We 1076 1-1/84.