Metastatic ocular melanoma to the liver exhibits infiltrative and nodular growth patterns

SummaryWe examined liver specimens from 15 patients with uveal melanoma (UM) who had died of their disseminated disease. We found 2 distinct growth patterns of UM metastasis: infiltrative (n = 12) and nodular (n = 3). In the infiltrative pattern, individual UM cells with a CD133+ cancer stem cell-like phenotype were present and formed aggregates of stage I <50-μm-diameter micrometastases in the sinusoidal spaces. These micrometastases appeared to expand, destroy adjacent hepatocytes, and form stage II 51- to 500-μm-diameter and then stage III >500μm-diameter metastases, which were encapsulated by collagenized fibrous septae. In the nodular growth pattern, CD133+ melanoma cells aggregated adjacent to portal venules and subsequently appeared to grow and efface the adjacent hepatocytes to form stage II 51- to 500-μm-diameter nodules that surrounded the portal venule. These avascular nodules appeared to further expand to form stage III >500-μm-diameter nodules that exhibited vascularization with minimal fibrosis. The tumor stem cell-like phenotype seen in individual UM cells was lost as the tumors progressed. There were CD56+ natural killer cells in sinusoidal spaces and CD3+ lymphocytes in periportal areas. The nodular growth pattern showed UM cells expressing MMP9 and VEGF. UM cells in both above-described growth patterns exhibited variable BAP1 expression. We propose that changes in the liver microenvironment are related to metastatic UM growth. We hypothesize that these changes include immune regulation within the sinusoidal space for the infiltrative pattern and changes in the VEGF/PEDF ratio for the nodular pattern.