Vascular volume in B16 allografts and human melanoma xenografts estimated by means of Hoechst 33342.

The vasculature of B16, a murine melanoma and Mel-mo, a human melanoma, was studied using intravital staining of patent capillaries by the fluorescent bisbenzamine dye Hoechst 33342. Capillaries were numerous at the edge of tumours in both the lines studied, but were scarcer within the nodules. Vascular volume as a proportion of total tumour volume was estimated by means of point counting. In both B16 and Mel-mo, the percentage vascular volume was inversely related to log tumour weight. Tumour necrosis, which increased with tumour size, was inversely correlated with percentage vascular volume, emphasizing the central under-perfusion of these experimental tumour nodules. This pattern of perfusion, with greater density of functioning capillaries at the periphery of tumour nodules, was seen in both the tumour lines examined despite differences in the degree and pattern of necrosis.