Are microscopic satellites in melanoma indicative of lymphovascular invasion? A preliminary case study

Microscopic satellites (microsatellites) in primary melanoma are defined as one or more discontinuous nests of neoplastic melanocytes measuring more than 0.05 mm in diameter that are clearly separated by normal dermis (i.e., no fibrosis or inflammation) from the main invasive component of the melanoma by a distance of at least 0.3 mm. Long considered an adverse prognostic variable, there has been debate about whether these satellites in fact represent lymphovascular invasion. In this preliminary study, 6 cases of primary cutaneous melanoma containing microsatellites were stained immunohistochemically for endothelial cells, using the markers CD31 and D2-40 (podoplanin, a marker of lymphatic endothelium). In none of the cases was positive staining found to surround the tumor deposits. In one case that also showed independent lymphovascular and perineural invasion, a small CD31 positive vessel within the microsatellite was found to contain tumor cells. The possible significance of these findings is discussed.