Masquerade Syndrome Revealing a Vitreous Metastasis from Adenosquamous Lung Carcinoma in a Patient Treated with Pembrolizumab

To describe the case of a 71-year-old man presenting with an isolated vitreous metastasis of an adenosquamous lung carcinoma treated with pembrolizumab. The patient initially presented with a unilateral visual loss (20/200) due to a dense vitritis. First-line treatment with oral corticosteroids 1 mg/kg was ineffective. A diagnostic vitrectomy was conducted, and cytological analyses were positive for malignancy with focal expression of TTF1 marker, confirming a secondary localization of his lung cancer. Adjunctive external radiotherapy (20 Gy/5 fractions) was performed due to an early recurrence and retinal extension. The evolution was marked by a neovascular glaucoma and a rapid progression of cataract. The patient underwent a combined surgery to remove the lens, apply pan-retinal photocoagulation, and fill the vitreous cavity with silicone oil. Six months after the surgery and the removal of the silicone oil, no metastatic recurrence occurred, and VA improved to 20/32. Vitreous metastasis is a rare condition, and vitreous metastatic extension of a lung cancer is even less frequent. We assume that Pembrolizumab, given to its high molecular weight and unaltered blood retinal barriers, failed to prevent the development of this secondary lesion. The origin of the lesion, choroidal or ciliary, remains unclear. Masquerade syndrome uveitis can may delay diagnosis and worsen outcomes. In case of failure of anti-inflammatory treatment, a cytological analysis should be conducted to confirm a tumoral origin.