A 56-year-old woman with a 4-year history of metastatic oestrogen-receptor-positive breast cancer (T2N1 invasive ductal carcinoma, treated with mastectomy and adjuvant therapy) presents with 3 weeks of painless blurred vision and metamorphopsia in the left eye. Visual acuity is 6/24 OS. Fundoscopy reveals a well-defined, creamy yellow-white subretinal mass superotemporal to the fovea with overlying serous retinal detachment. The structure marked **A** in the diagram is non-pigmented and shows medium-to-high internal reflectivity on B-scan ultrasound. Which of the following BEST characterizes this lesion and distinguishes it from primary choroidal melanoma?