Vascular invasion in malignant melanomas. An independent prognostic variable?

The role of vascular invasion as a prognostic indicator in melanoma has not been fully evaluated, mainly due to difficulty in differentiating between capillaries and artefactual spaces caused by shrinkage in routine histological sections. However, immunohistochemical staining using Ulex europaeus I (UEA-I) permits accurate identification of tumor capillaries, thus facilitating recognition of vascular invasion. Sixty-six primary cutaneous melanomas were included in this study. Sections of each case were stained with UEA-I; then, vascular invasion at the level of the tumor capillary bed was sought. Hematoxylin-and-eosin-stained sections were reviewed; the thickness of each lesion was measured and the level of invasion and the growth phase of the tumors were also assessed. The frequency of vascular invasion was found to increase with increasing tumor thickness and with increasing level of invasion. Vascular invasion was seen in only one of 29 horizontal growth phase melanomas, whereas it was identified in 28 of 37 vertical growth phase tumors. Although these results would seem to indicate that vascular invasion within melanomas is unlikely to be an independent prognostic variable, they may partly explain the deteriorating prognosis associated with increasing tumor thickness. They also lend support to the concept of "horizontal" and "vertical" growth phase in melanoma.