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Background
Breast cancer has varied presentations on imaging. Furthermore, not all breast cancers are identified on all imaging modalities. Digital mammography (DM) and digital breast tomosynthesis (DBT) are the most common screening tools used in detection of breast cancer. DBT has lower recall rates and higher cancer detection rates, particularly in young women and in women with dense breasts. In first round screening, DM has a cancer detection rate of 4.5 per 1000 screening mammograms. In comparison to DM, DBT finds an additional 0–2 cancers per 1000 mammograms, screening ultrasound finds an additional 3–4 cancers per 1000 mammograms, and MRI detects an additional 16 cancers per 1000 mammograms. The existing screening and diagnostic guidelines are aimed at utilizing the unique strengths of each imaging modality in the appropriate patient subset. This case-based review of breast cancers identified on different imaging modalities will help residents understand the merits and demerits of DM, DBT, ultrasound, and MRI.

Educational Goals / Teaching Points
As breast density increases, the sensitivity of DM and DBT decreases, more so in DM. However, even in women with less dense breasts, DBT enables detection of small cancers. High grade invasive breast cancers can also present as equal to low density masses, with circumscribed margins. In a woman aged 30 or above, a palpable breast lump is evaluated by ultrasound (even if there is no mammographic correlate), because ultrasound can sometimes identify masses not visible on a mammogram. In a woman with spontaneous, unilateral, clear, or bloody nipple discharge, whose mammogram and ultrasound are negative, further evaluation by MRI can help in identifying the etiology. Not all ductal carcinoma in situ (DCIS) present as suspicious morphology calcifications; breast MRI can identify DCIS that hide in plain sight on the mammogram. The accuracy of breast MRI in evaluating residual tumor size following neoadjuvant chemotherapy depends on tumor phenotype, morphology, and biomarker status. Even a complete radiologic response to neoadjuvant chemotherapy on a breast MRI can still reveal a large area of residual cancer on pathology.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The key imaging findings are highlighted via case-based examples.

Conclusion
The goal of this presentation is to demonstrate the strengths and limitations of the main imaging modalities used in screening and diagnosis of breast cancer. Understanding the effective use of the main imaging tools in the diagnosis of breast cancer will enable early detection.