Surgical resection of intraorbital metastasis of a gastrointestinal stromal tumor resistant to chemotherapy.

[PURPOSE] We present a case of a gastrointestinal stromal tumor (GIST) metastasis of the rectal primary resisting chemotherapy to the right orbit 15 years after excision of the primary lesion.

[OBSERVATIONS] A 79-year-old man was diagnosed with rectal GIST at the age of 65 years and underwent rectal amputation. He underwent hepatectomy for GIST liver metastases at the age of 69 years and pericardiectomy for GIST pericardial metastases at 72 years of age. At the age of 79 years, positron emission tomography-computed tomography revealed the possibility of liver metastasis and metastasis to the right orbit of 10 mm in size. Magnetic resonance imaging revealed a well-circumscribed mass of 10 mm × 12 mm in the deep medial rectus muscle of the right orbit, which was referred to our department for ophthalmic examination. The latter revealed only mild abduction disorder in the right eye. Although chemotherapy was initiated, the tumor gradually increased, causing exophthalmos in the right eye, visual field impairment due to optic nerve exclusion, and decreased visual acuity. Due to repeated multiple metastases, the patient underwent right orbital exenteration and free flap reconstruction at the age of 83 years for radical cure. Pathological examination revealed c-Kit positive, CD34 positive, S100 protein minority positive, MIB-1 positive rate of 10% or more, and α-SMA negative, and the diagnosis was intraorbital metastasis of GIST.

[CONCLUSIONS AND IMPORTANCE] Orbital metastases in GISTs are extremely rare, and there is no established standard treatment. Therefore, a comprehensive decision must be made based on the final treatment goal and the patient's background when selecting treatment.