Follow up of a slowly growing melanocytic lesion during 12 years

Purpose We report an atypical case of a very slowly growing and rather flat pigmented lesion in the posterior pole. Methods A women 53 years old at presentation, was followed during more than 12 years for a posterior pole lesion. Periodical fundoscopy, fluoangiography, ICG angiography and ultrasounds were performed. After enucleation in 2008, the definitive diagnosis was made after histopathologic examination. Results Visual decrease because of macular oedema in the left eye was the reason for referral. Fundus examination and fluo-angiography revealed a slowly enlarging subretinal lesion with abnormal pigmentation and leakage with signs of chronic neurosensory detachment; ultrasound examination showed a cystic lesion with macular oedema. The lesion increased very slowly in thickness until a maximum of 1.5mm. Finally a chronic retinal detachment caused an intractable neovascular glaucoma and necessitated enucleation in 2008. Histopathology showed a diffuse proliferation of small spindled melanocytes with bland, uniform nuclei lacking mitotic activity with some small nests of larger, haevely pigmented epitheloid melanocytes with nuclear pleimorphism, embedded in collageneous matrix. The cell proliferation marker Ki67 showed only rare tumor cells with immunoreactive nuclei,indicating a very low fraction of cycling tumor cells. Other immunohistochemical markers are currently performed in order to elucidate the biological behaviour. Conclusion This case shows a unusually slowly growing lesion with classical histological features of melanoma and suggests the existence of a type of ocular melanoma of extremely low grade malignancy. Further phenotypical profiling is warranted in order to understand the cause of this "benign" behaviour.