Primary Conjunctival Pigmented Basal Cell Carcinoma with Increased Numbers of Intra-Tumour Melanocytes, Mimicking Melanoma: A Case Report and Review of the Literature.

A 60-year-old, South-Asian male patient presented with a dark brown lesion on his left conjunctiva surface near the limbus for 2 years. Examination showed a globular, dark brown-coloured mass near the temporal limbus at 4 to 5 o'clock position, measuring 3 × 3 × 2 mm. There were a few scattered flat pigmented lesions near the mass and also a few prominent vessels. The mass underwent wide local excision, with a clear margin, followed by double freeze cryotherapy of the conjunctival margins along with the application of Mitomycin C. The bare sclera was covered by amniotic membrane. Histology surprisingly revealed a nodular basal cell carcinoma (BCC) containing melanin. The melanin was present in the tumour cell cytoplasm, within melanophages and within dendritic, Melan A-positive melanocytes. The BCC was immunohistochemically positive for BerEP4 and negative for EMA. The clinically observed smaller nodules flanking the main pigmented BCC corresponded histologically to pigmented superficial growth pattern BCC connected to the under surface of the conjunctival epithelium. This is the first report of a pigmented BCC of the conjunctiva, mimicking a conjunctival melanoma. Pigmented BCC should be considered in the differential diagnosis of pigmented tumours of the conjunctiva.