Metastatic disease to the breast is uncommon and represents less than 2% of all breast malignancies. Sources of metastases include carcinoma of the opposite breast, lymphoma, leukemia, and melanoma. In children, rhabdomyosarcoma is the most common cause while in males prostatic adenocarcinoma is the most common culprit.
Metastases to the breast differ from primary breast carcinoma in that chest wall fixation, skin/nipple retraction, spiculations, and microcalcifications are generally not seen. Metastases are more like to be multiple and bilateral than primary malignancies.
There are two mechanisms of occurrence of metastases to the breast: lymphangitic and hematogenous spread. The former occurs across the anterior thoracic wall with the contralateral breast as the source. This gives an appearance of dense subcutaneous fat with thickened trabecular pattern. As the tumor spreads via lymphatics, the glandular stroma of the breast also appears dense and irregular. This appearance is indistinguishable from that of inflammatory breast carcinoma and is most commonly seen with metastases from the contralateral breast and gastric carcinoma. A solitary discrete lesion is the most common appearance of hematogenous metastases to the breast.
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Lee SH, Park JM, Kook SH, et al. Metastatic tumors to the breast: mammographic and ultrasonographic findings. J Ultrasound Med. 2000;19:257-62.