Imaging diagnostics of breast metastases from extramammary tumors

: Breast metastases of solid extramammary tumors are very rare in comparison to primary malignancies of the breast and account for only 0.33-6.3% of all malignant neoplasms of the breast. The most common primary tumors are malignant melanoma, distant sarcomas, lung cancer, ovarian cancer, renal cell cancer and thyroid cancer in decreasing order of frequency. This review article summarizes the clinical features and the different imaging findings of breast metastases from different extramammary solid tumors. Breast metastases are often incidental findings in computed tomography (CT) or positron emission tomography CT (PET-CT) imaging. Mammography shows two different imaging patterns, namely focal lesions and diffuse architectural distortion with skin thickening. Breast metastases presenting as focal masses usually occur as solitary and more rarely as multiple round lesions with a smooth edge boundary. Associated calcifications are rare findings. Diffuse architectural distortion with skin thickening is more common in breast metastases from most gastric tumors, ovarian cancer and rhabdomyosarcoma. Using ultrasound most lesions are hypoechoic, oval or round with smooth boundaries and posterior acoustic enhancement. The magnetic resonance imaging (MRI) criteria of breast metastases show an inconstant signal behavior that cannot be safely classified as benign or malignant. In summary, in patients with known malignancies the presence of breast metastases should be considered even with imposing clinically and radiologically benign findings.