Extravascular Migratory Metastasis (Pericytic Mimicry) in Sarcomatoid Squamous Cell Carcinoma of the Vulva: A Report of 2 Cases.

Extravascular migratory metastasis (EVMM), also known as pericytic mimicry or angiotropism, is a mechanism of angiocentric tumor spread that has been investigated mainly in cutaneous malignant melanoma where it has been associated with an increased risk of metastasis. In EVMM, the tumor cells spread along the external (ablumenal) aspect of vessels without breaching the endothelium, a process that is therefore distinct from the more widely recognized intraluminal invasion. Although EVMM has also been reported in a limited range of other tumor types, to our knowledge it has not been described in squamous cell carcinoma (SCC). Herein we report EVMM in 2 cases of sarcomatoid SCC of the vulva. The tumors arose in patients aged 78 and 61 yr both of whom had previous histories of histologically conventional vulval SCCs occurring in a background of lichen sclerosus and differentiated-type vulval intraepithelial neoplasia. Both tumors recurred leading to fatal metastasis in 1 patient and a requirement for pelvic exenteration in the second. Intravascular tumor involvement was not identified in either case. These cases support the view that sarcomatoid SCCs of the vulva are clinically aggressive neoplasms, and EVMM may contribute toward the risk of local and distant spread in these tumors.