NUT Carcinoma of the Lacrimal Apparatus Presenting as a Rapidly Enlarging Medial Canthal Mass: A Case Report.

IntroductionNUT carcinoma (NC) is a rare, aggressive squamous-lineage malignancy characterized by NUTM1 gene rearrangement and distinctive nuclear NUT expression by immunohistochemistry. Ocular adnexal involvement is exceptional.Patient presentationA 26-year-old woman presented with redness, pruritus, and a large nasal canthal mass obstructing vision in the left eye. Examination showed a 4 × 3 cm lacrimal mass extending into the extraconal orbit with extraocular muscle compression. Histology showed nests of small round blue cells with crush artifact and abrupt keratinization. Immunohistochemistry demonstrated diffuse pan-keratin, p63, p40, and speckled nuclear NUTM1 positivity; CD99 and NKX2.2 were negative-confirming NC.ConclusionLacrimal sac/gland NC should be considered in rapidly enlarging medial canthal masses in young patients. Prompt biopsy with IMMUNOHISTOCHEMISTRY for NUT and early multidisciplinary management are critical.