Lymphatic invasion revealed by multispectral imaging is common in primary melanomas and associates with prognosis.

Lymphatic invasion by tumor cells has been noted infrequently in primary melanomas. Our primary hypotheses were that using immunohistochemical markers of lymphatic vessels and of tumor cells would improve detection of lymphatic invasion and that lymphatic invasion would correlate with regional nodal metastatic disease. This study included 106 patients who were diagnosed between 1972 and 1991 and who had 10 years or more of follow-up. We performed dual immunohistochemical stains for podoplanin (for lymphatic vessels) and S-100 (for melanoma cells). Lymphatic invasion was identified by light microscopy and confirmed by multispectral imaging analysis. Lymphatic invasion was detected by morphology alone in 5 cases (4.7%) in contrast to immunohistochemical staining augmented by multispectral imaging analysis where 35 cases (33%) were identified (P < .0001). Lymphatic invasion was significantly associated with time to regional nodal metastatic disease, as well as first metastasis and melanoma-specific death. "Local metastasis," defined by immunohistochemistry-detected lymphatic invasion, satellites, or neural invasion, identified 64% of those who had regional nodal metastatic disease within 5 years of diagnosis. Lymphatic invasion is an underobserved phenomenon in primary melanomas that can be better detected by immunohistochemical staining. The presence of lymphatic invasion may be a clinically useful predictor of regionally metastatic disease.