Purpose: Fibroglandular tissue may mask breast cancers, thereby reducing the sensitivity of mammography. Here we investigate methods for identification of women at high risk of a masked tumor, who could benefit from additional imaging. Methods: The last negative screening mammograms of 111 women with interval cancer (IC) within 12 months after the examination and 1110 selected normal screening exams from women without cancer were used. From the mammograms volumetric breast density maps were computed, which provide the dense tissue thickness for each pixel location. With these maps, three measurements were derived: 1) Percent dense volume (PDV), 2) Percent area where dense tissue thickness exceeds 1cm (PDA), 3) Dense Tissue Masking Model (DTMM). Breast density was scored by a breast radiologist using BI-RADS. Women with heterogeneously and extremely dense breasts were considered at high masking risk. For each masking measure, mammograms were divided into a high and low risk category, such that the same proportion of the controls is at high masking risk as with BI-RADS. Results: Of the women with IC, 66.1%, 71.9%, 69.2% and 63.0% were categorized to be at high masking risk with PDV, PDA, DTMM and BI-RADS respectively, against 38.5% of the controls. The proportion of IC at high masking risk is statistically significantly different between BI-RADS and PDA (p-value 0.022). Differences between BI-RADS and PDV, or BI-RADS and DTMM, are not statistically significant. Conclusion: Measures based on density maps, and in particular PDA, are promising tools to identify women at high risk for a masked cancer.
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