Metachronous, non-pineal, trilateral retinoblastoma in a patient with a seemingly reduced-expressivity RB1 germline deletion.

The clinical course of trilateral retinoblastoma can be unpredictable, and expressivity of germline RB1 variants may vary during development. We describe an unexpected fatal case of trilateral retinoblastoma with an intracranial tumor in an unusual location and discuss genetic copy number analyses as a useful diagnostic tool with therapeutic potential.