Background: To evaluate semiautomated quantitative analysis of the BPE in postmenopausal women who were diagnosed breast cancer and to correlate it with mammographic breast density and aggressiveness of the primary cancer. Methods: Informed patient consent was waived after institutional review board approved this study. Four hundred eighty two breast cancer patients performed breast MRI in our institution during 16 months, and 84 postmenopausal women of them were included in this study (median age, 67.2 years; range, 60-76 years). Ordinary values of BPE and breast density were described by an experienced breast radiologist using the BIRADS lexicon. The BPE was calculated with semiautomated quantitative method for quantitative analysis: BPE coefficient (BEC = SI₁-SI₀ / S₀ × 100), where SI is signal intensity, SI₁ is the SI enhancement measured in the largest dimension of the sagittal plane at the first postcontrast image, and S₀ is the SI before contrast injection. On surgical pathology, pathologic subtype, nuclear and histologic grade, estrogen receptor (ER), progesterone receptor (PR), HER2≠neu, venous and lymphatic invasion, lymph node metastasis was evaluated. And then, the mean BEC of the patients who diagnosed local or systemic recurrence on follow-up was calculated and compared with that of the patients without recurrence. The statistical analysis was performed using Kruskal-Wallis test and Mann-Whitney U test. Results: The mean BEC of the postmenopausal women was 3.96 ± 6.71 in right breast and 3.41 ± 8.09 in left breast. There was no significant difference in the BEC between mammographic breast density groups (P > 0.05). There was no significant correlation between BPE and aggressiveness of the primary breast cancer. However, the mean BEC was higher in the recurrent patient group (n = 6, mean=16.23 ± 19.88) compared with the patients without recurrence (n = 78, mean=2.44 ± 5.62). Conclusions: No association was found between BPE and aggressiveness of the primary breast cancer, BPE and breast density. However, the mean BEC was higher in the patients who diagnosed local or systemic recurrence.