Abstract
Two patients, with non-small cell lung carcinoma treated with pembrolizumab, developed bilateral diffuse uveal melanocytic proliferation (BDUMP) with interesting histopathological features. The first patient developed a right ciliary body mass concurrently with BDUMP. The globe was enucleated. The ciliary body mass was a mitotically active epithelioid uveal melanoma, invading the trabecular meshwork and peripheral corneal stroma, with over 90% of the cells expressing Cyclin D1 protein. The melanoma showed no chromosome 3 or 8 changes. The background uvea showed diffuse, bland spindle cell melanocytic proliferation with much lower Cyclin D1 expression (around 10%). In the choroid, this population was punctuated by islands of pigmented epithelioid cells, some of which were necrotic. All these islands expressed a high level of Cyclin D1, and some islands expressed nuclear preferentially expressed antigen in melanoma (PRAME). The ciliary body mass, epithelioid cell islands, and the BDUMP all expressed c-Met (the receptor for hepatocyte growth factor [HGF]). The features were those of ciliary body melanoma and choroidal melanoma "tumorlets," developing on a background of BDUMP. The second patient developed bilateral periocular skin pigmentation following a diagnosis of BDUMP, which when biopsied, showed dermal islands of paraneoplastic perivascular melanocytic cell proliferation. These cells also expressed c-Met protein. These observations implicate the HGF/c-Met axis in the pathogenesis of BDUMP, the uveal melanomas in the ciliary body and choroid in the first patient and the paraneoplastic dermal melanocytic proliferation in the second patient.