Diffuse Amelanotic Choroidal Melanoma Mimicking Mushrooming Melanocytic Melanoma and Choroidal Metastasis in a Patient with Dual Primary Malignancies: A Case Report.

Introduction: Choroidal melanoma is the most common primary intraocular malignancy in adults, whereas ocular metastases are the most frequent overall intraocular tumors. Diffuse amelanotic choroidal melanomas are rare and may mimic metastatic lesions, particularly in patients with known systemic malignancies. Optic nerve invasion is an uncommon but clinically significant feature of advanced melanoma. Case Presentation: We report an 82-year-old male with a history of recurrent cutaneous melanoma and stage III rectal carcinoma who presented with progressive vision loss in the right eye. Fundus examination revealed a peripapillary elevated hemorrhagic mass and a flat tan choroidal lesion. Multimodal imaging suggested a differential diagnosis of choroidal metastasis versus melanoma. Intraocular biopsy confirmed diffuse amelanotic choroidal melanoma. Enucleation revealed mixed cell-type melanoma with optic nerve invasion and extrascleral extension. The patient later developed systemic metastasis from the ocular melanoma. Conclusion: Diffuse amelanotic choroidal melanoma can closely mimic metastatic disease, especially in patients with known primary cancers. Intraocular biopsy remains essential for definitive diagnosis in ambiguous cases and guides appropriate oncologic management.