The inverse relationship between microvessel counts and tumor volume in breast cancer.

Angiogenesis has emerged as an indicator of metastatic potential in invasive breast cancer. Exponential tumor growth and the appearance of metastasis are observed as new microvessels form. We postulated that the relevance of angiogenesis would be enhanced if analyzed as a function of tumor volume rather than greatest diameter alone and that microvessel counts would proportionately increase as does volume. Since tumors are three-dimensional solids, volume was calculated using the formula for an ellipsoid, V = pi/6 (a x b x c). Sixty-four tumors < or = 2.5 cm were studied and analyzed in 5 mm incremental ranges. Mean microvessel counts did not vary significantly among these tumor size groups. However, analysis of microvessel counts as a function of tumor volume decreased from 947.1/cm3 (0-0.5 cm) to 18.1/cm3 (2.1-2.5 cm), a greater than 50-fold difference. High microvessel density in small cancers supports the notion of metastasis as an early event, making these small tumors perhaps ideal targets for antiangiogenic agents.