Morphology of angiogenesis in human cancer: A conceptual overview, histoprognostic perspective and significance of neoangiogenesis

This paper reviews the histomorphological aspects of angiogenesis and neoangiogenesis, quantitative and qualitative, and their applications in prognostic evaluation of neoplastic diseases. The merits and weak points of intratumoral microvessel density (MVD), a widely regarded bona fide predictor of tumour growth, metastases and patient survival, are discussed. Total microvascular area (TVA) has been found useful in recent prognostic studies utilizing newer immunohistochemical vascular markers. Of particular significance is the fact that MVD and TVA are most predictive of patient outcome in those tumours that induce significant neoangiogenesis, namely carcinomas of breast and prostate, and haematological malignancies. In contrast, carcinomas of lung and urinary bladder do not show significant associations of MVD and TVA with poor prognosis, reflecting differences in angiogenic mechanisms. In gliomas, MVD appears to correlate with outcome in high-grade, but not low-grade tumours, and does not correlate with tumour cellularity in the infiltrating portions of the tumour, reflecting a paucity of neoangiogenesis and directional vascular growth. Recent studies have found CD105, Tie-2/Tek and vascular endothelial growth factor receptors to be the best markers of neoangiogenesis. The vascular parameters so measured correlate better with overall and disease-free survival in breast, colon and lung carcinoma than panendothelial markers such as CD31. A correlation of vascular patterns with prognosis has been established in ocular melanomas, glioblastomas and squamous carcinomas of head and neck region. Vascular networks with closed loops are closely associated with mortality due to metastases in uveal melanomas. Fewer bizarre glomeruloid vessels and prominent classical capillary pattern was an independent predictor of longer survival in glioblastoma. Therefore a judicious combination of quantitative and qualitative microscopic angiogenic parameters, with emphasis on neoangiogenesis and vascular patterns wherever applicable, should be an integral component of a more consistent tumour staging system for accurate prognostic evaluation of tumours, selection of optimal anti-angiogenic therapy and pertinent research.