Objective:To observe the histopathological changes of transplanted rabbit breast tumor treated with high intensity focused ultrasound (HIFU).Methods:Forty-two experimental rabbits were divided into HIFU group (n=35)and control group(n=7)

HIFU ablation was completely performed in the HIFU group with ultrasound imaging guidance

and the pathological changes were examined immediately and on 1st

3rd

7th

14th

21st

28th day after HIFU treatment.Results:The target area of tumor appeared gray immediately after HIFU treatment;the morphology and arrangement of the cellular nucleus showed no obvious alteration in HE stained sections after HIFU ablation;however

electron microscopy revealed that the cellular membrane and nuclear membrane was rupturing

cell organelle destructed and appearance of vacuolus without membrane in cytoplasm;Enzyme histochemical staining showed that the succinate dehydrogenase (SDH)in target area of tumor disappeared

also the proliferating cell nuclear antigen (PCNA)was negative examined by using immunohistochemical staining

suggesting the death of tumor cells;The coagulative tissue got liquefied and absorbed with the extension of time

then it was substituted by fibrous tissue finally. Conclusion:HIFU can effectively destroy the transplanted rabbit breast tumor

it provided referred value for clinical application of HIFU in the treatment of breast cancer.