Embryonic Vasculogenesis in Nodular Melanomas and Tumour Differentiation

The relationship of vasculogenic mimicry to pigment in nodular vertical growth phase VGP] cutaneous melanomas is assessed in this study. 10 nodules each from 27 tumors, 15 pigmented and 12 amelanotic were sampled in proportion to the pigment level. Serial frozen and paraffin sections subjected to HE, Reticulin, PAS to assess the vascular pattern; Dopa Oxidase and Immunopositivity for HMB45, LN5 laminin 5] & integrinα₅β₁], and EM electron microscopy] to identify Weibel-Palade bodies within endothelial cells. The vascular pattern, pigment and the immunopositivity was mapped to assess the percentage VM vasculogenic sinusoids] vs INC incorporated microvasculature]. In pigmented melanomas, INC from pre-existing stromal vessels is predominant. Amelanotic melanomas show embryonic vasculogenic mimicry, a self-propagating system of spaces within the sheets of tumors cells. Both INC and VM co-exist in tumors with both amelanotic and melanotic nodules. In areas with VM, loci of LN5 and α₅β₁ integrin positive cells appear within the proliferating columns, positivity in these cells suggesting a switch to a more aggressive form. Irregular spaces appear lined by tumor cells, with initial hemopoeitic activity, coalesce and interlink into tubular networks. Spaces lined by tumor cells extend into an intricate network which then connects with the angiogenetic system. The tumor cells lining the vasculogenic spaces are positive for LN5, α₅β₁ integrin. Statistically, INC is significantly higher in pigmented melanomas, whereas amelanotic melanomas show significantly higher VM. Pigmentation is correlated positively with INC and negatively with VM. INC and VM are negatively correlated with each other.