Background: One of the greatest challenges in breast cancer management is to accurately predict the outcome for each patient. Microvessel density (MVD) correlated closely with increasing number of tumor cells shed into the bloodstream and development of metastasis. Because proliferation status closely correlates with tumor aggressiveness, proliferation index (PI) is considered as an established prognostic marker for various tumors. We aimed to: 1. Study MVD and PI by assessing immunohistochemical profiles of CD31 and Ki67 respectively and their probable role in breast cancer progression. 2. Assess values of CD31 and Ki67 in relations to clinico-pathological prognostic parameters. Subjects and methods: Immunostaining was done to detect CD31 and Ki67 expressions in 74 specimens of breast lesions. Results: Both CD31 and Ki67 increased progressively along the continuum of neoplastic changes from normal breast epithelium to invasive ductal carcinomas; IDC (P<0.000 for each). CD31 expression was positively correlated with tumor size (p< 0.04), increasing grade (P <0.01), lymphovascular invasion (p<0.01) and lymph node metastasis (P<0.05) in IDC. There was significant positive correlation between Ki67 expression and increasing grade (P<0.03) and lymph node metastasis (P<0.02) in IDC. Positive correlation was present between Ki67 and CD31 in ductal carcinoma in situ (DCIS) and in IDC (P<0.02 & P<0.001 respectively). Conclusion: Our findings indicate that aggressive tumors are more capable of angiogenesis and proliferation which are poor prognostic signs in IDC. These findings might open the door for new therapeutic strategies to prevent progression of DCIS to IDC.