The choroid is definitively established as the lymphoma origin through converging evidence including temporal precedence of visual deterioration over systemic anemic manifestations, histopathologic confirmation of extranodal marginal zone B-cell lymphoma exhibiting CD20+ and Ki67 < 5% without anterior segment involvement in the enucleated mass, PET-CT exclusion of alternate primaries showing no metabolically active lesions in lymph nodes, spleen, or visceral organs, and bone marrow biopsy revealing EMZL morphologically and immunophenotypically identical (CD5−/CD10−) to the choroidal tumor. The gene discussed is MKI67; the disease is MALT lymphoma.