The accuracy of breast cancer staging involves the estimation of the tumor size for the initial decision-making in the treatment. We investigated the accuracy of tumor size estimation and the association between tumor characteristics and breast density (BD).

Materials and methods

A total of 434 women with a primary diagnosis of breast cancer were included in this prospective study at a specialist breast unit. Estimated tumor characteristics included tumor size, nodal status, estrogen/progesterone receptor status, Ki-67, HER2/neu, vascular invasion. Radiomorphological data included tumor size as assessed by mammography, breast ultrasonography, and clinical examination, and American College of Radiology (ACR) categories for BD.

Results

BD did not have a significant impact on the assessment of tumor size using breast ultrasound (deviation from ACR categories 1–4: 0.55–0.68 cm; P = 0.331). The deviation in mammography was significantly different dependent on BD (0.42–0.9 cm; P < 0.001). The clinical examination was not affected by BD. Age and tumor size were the only parameters associated with a denser breast in the multivariate analysis. Older women were less likely to have dense breasts (odds ratio 0.157 for women aged ≥70 years), and patients with larger tumors were less likely to have dense breasts (adjusted OR 0.36 for tumors > 2 cm).

Conclusion

Breast ultrasonography is more accurate than mammography for assessing tumor size in breasts with a higher BD. The difference in tumor size assessment needs to be taken into consideration in the design of clinical trials and treatment decisions.