The microvasculature of the 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumour. I. Vascular patterns as visualized by scanning electron microscopy of corrosion casts.

We examined the microvasculature of the 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumour by scanning electron microscopy of corrosion casts. An elaborate vascular envelope predominantly consisting of sinusoidal and venular vessels was formed around each tumour nodule. These vessels exhibited various abnormal features, whereas arterioles appeared normal. The abnormal vessels possessed many globular outpouches, possibly representing the site of angiogenesis. An additional capillary layer was seen in the marginal boundary between the tumour and host tissue. The lack of centrifugally extruding vessels in this layer may indicate a poor potency for vascular spread of tumour cells into the adjacent normal tissue. Loop-like or glomerular ingrowths were frequently found on the inner aspect of the vascular capsule, which eventually developed into a dense intranodular plexus. Intranodular vessels often showed focal narrowing, tapering and/or rupturing, possibly due to increased tissue pressure caused by proliferating tumour cells. Those surrounding necrotic portions were extremely dilated with occasional periodic varicosities. The features may be associated with the lessening of the tissue pressure resulting from tumour cell collapse.