Abstract

DO.08.04

Histological findings of a choroidal melanoma one year after proton beam irradiation

Stefan Koinzer1, Heike Hasselbach1, Jan Hinrich Bräsen2, Ivo Leuschner2, Johann Roider1
1Klinik für Ophthalmologie, Campus Kiel, Universitätsklinikum Schleswig-Holstein, Kiel; 2Pathologie, Campus Kiel, Universitätsklinikum Schleswig-Holstein, Kiel

Objective
Choroidal melanomas constitute a large group among intraocular tumors. If they are not too large and don't infiltrate extraocular structures, irradiation is the first line therapy. If the tumor is located centrally, proton beam irradiation may be preferred over brachytherapy because of less colateral damage. Little is known about the histological findings after proton beam therapy. We report on histological findings one year after proton irradiation of a malignant choroidal melanoma.
Methods
A 52 year old female patient was treated by proton beam irradiation of an amelanotic choroidal melanoma located at the superior arcade in her right eye. At the time of diagnosis, a neuroendocrine tumor of the ileum had been diagnosed 6 months ago which had seeded into the liver and lymph nodes. Thus a choroidal metastasis of this tumor was considered a differential diagnosis. One year after proton irradiation, the choroidal tumor showed subtle growth. For this reason and because of the histologically uncertain origin of the tumor, a transretinal biopsy was performed. Consecutive follow up examinations did not show any further tumor growth over 6 months.
Results
Histological specimens of the tumor biopsy showed fibrous tissue containing spindle cells, some of which contained fine granular pigment. These cells stained positively for melan A and HMB 45, but did not stain for synaptophysin. Ki-67 stained single nuclei according to a very low proliferation rate of <1%. Tumor regression could not be determined by certainty. Degraded cells or apoptosis bodies were not present. However, sclerosis was abundant.
Conclusions
Histologically, the choroidal tumor was a melanoma. A metastasis of the neuroendocrine tumor could be excluded. One year after proton irradiation, the melanoma still contained morphologically viable cells. The proliferation rate was low, a finding which may also show in untreated malignant melanomas. The tumor tissue might have entered a "silent phase" through proton irradiation. The clinical follow up visits have not shown signs of tumor reactivation during 6 months after tumor biopsy.

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