Abstract: Objective To study the clinical and histological characteristics of fibrosarcoma caused by postoperative radiotherapy for pituitary adenoma. Methods We analyzed a case of post-irradiation fibrosarcoma 8 years after surgery followed by irradiation for pituitary adenoma. Results The patient underwent transsphenoidal resection of the recurrent tumor. This led to significant relief in the patient's symptoms, but the tumor recrudescent a year later original. Humor was histologically verified to be a well differentiated fibrosarcoma(NCI grading system Ⅰ). The recrudescenttumor had high grade characteristics as a poorly differentiated fibrosarcoma(NCI grading system Ⅲ). The tumor cells responded positively in response to immunohistochemical staining for vimentin, but negatively for pan-CK, S-100, SMA, GFAP(-), CD117, GH, PRL, LH, FSH, TSH, ACTH. Conclusion Radiotherapy for pituitary adenomas can rarely induce fibrosarcomas. They should be suspected in patients following sellar irradiation who show abrupt new symptoms and has appropriate radiological findings. The secondary tumors are easy to regrow and the prognosis is poor.

Key words: pituitary adenoma, radiotherapy, fibrosarcoma, secondary tumor