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Choroidal melanoma.
Ocular melanoma can be divided into two large categories: uveal and conjunctival melanoma. Uveal melanoma is further categorized into those arising from choroid, ciliary body or the iris. Choroidal melanoma is the most common ocular melanoma. Conjunctival melanoma is a very rare entity.
Uveal and non-uveal melanomas are also molecularly distinct entities. BRAF mutation is almost never seen in uveal melanoma, while present in about 30-40% of conjunctival melanoma. Mutations in GNAQ appear to be the most common in uveal melanoma. In cases with family history of mesothelioma and uveal melanoma, germline mutations in BAP1 should be considered. BAP1-mutated melanocytic tumours also include atypical spitzoid lesions.
The cells that comprise this lesion are categorized into spindle and epithelioid cells. In uveal melanoma, this categorization is synonymous with grading of the lesion; those composed of > 90% spindle cells is graded as Grade 1 (“Spindle cell melanoma”), with Grade 3 lesions being comprised of > 90% epithelioid cells. Many cases would be categorized as “mixed” cell types (Grade 2), as in this case, where > 10%-90% of the cells are epithelioid cells. The epithelioid and spindle cells appear to differ in their metastatic potential.
See LMP19808 - Choroidal melanoma for another example of this entity (see link in related content).