Mammographic density reflects comprehensive changes in the mammary gland. The condition of the tumour microenvironment is a possible factor affecting tumour progression, as well as a tumour risk factor. This study aimed to determine whether mammographic density correlates with tumour clinicopathological features and prognosis in breast cancer patients. The analysis involved 163 Japanese women who underwent surgery for breast cancer between 1999 and 2003 in the Nagasaki University Hospital, Japan. Mammographic density was classified according to the breast imaging reporting and data system (BI-RADS) categories 1-4. Age, tumour size, axillary lymph node involvement, steroid receptor (SR) status, histological grade and Nottingham prognostic index (NPI) were analysed by density category and tested for statistically significant differences across categories. A significant difference (P<0.05) by breast-density category was found only for age. SR-negative tumours had significantly worse NPI scores than SR-positive tumours in breast-density categories 2 (P=0.03) and 4 (P<0.001). A high distant-metastasis frequency was observed in category 4 SR negatives (44%) versus category 4 SR positives (4.3%). These findings reveal that although the BI-RADS breast-density category alone is not associated with prognosis in breast cancer, patients who are both category 4 and SR negative have an extremely poor prognosis.

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