PGR and breast neoplasm: After investigating the correlation between color power Doppler sonographic measurement of breast tumor vasculature and immunohistochemical analysis of microvessel density for the quantitation of angiogenesis, Yang et al.44 found that higher microvessel density was noted in malignant than benign breast masses (P < 0.0005) and that tumor vessel numbers were in a significant positive correlation with tumor size (P < 0.05) and progesterone receptor negativity (P < 0.05).