Metastases to the breast

Metastases to the breast from non-mammary primary tumors are uncommon and account for 0.5-2.0% of all breast malignancies. 

Clinical presentation

Metastases do not tend to cause retraction of the skin or nipple. Metastatic lesions are much more likely to be multiple or bilateral than primary cancers. 

Pathology

Breast metastases from extra-mammary malignancies are unusual, and if present, typically indicate widely disseminated disease. They tend to be found in the subcutaneous fat, whereas primary breast cancers develop in glandular tissue.

Primary sites

The most frequent source of a metastatic breast lesion is the contralateral breast ². The most common extra-mammary cancers that metastasize to the breast are:

• lymphoma/leukemia: most common extramammary source ²
• melanoma
• sarcomas
• prostate cancer: considered on the most frequent primary sites in men ⁴
• lung cancer
• gastric cancer
• ovarian cancer
• renal cell cancer
• malignant mesothelioma ⁵
• carcinoid tumor ⁶
• carcinoma of the cervix ⁷
• rectal cancer ⁸
• papillary thyroid carcinoma ⁹

Radiographic features

Like other metastasis, metastases to the breast tend to be rounded and well defined. As opposed to breast cancer, calcification is unusual.

Mammography

On mammography, metastatic lesions may manifest as single or multiple masses or as diffuse skin thickening. Metastases usually appear as round masses with circumscribed or ill-defined borders. They typically lack spiculation. Microcalcifications are rare can occur with some primary type (e.g, psammoma bodies in ovarian cancer).

Ultrasound

On ultrasound, metastatic masses tend to have circumscribed margins with low-level internal echoes and, occasionally, posterior acoustic enhancement. Color Doppler interrogation most often shows increased vascularity.

History and etymology

The first case of a metastatic lesion to the breast is thought to have been reported by Trevithick in 1903 ⁴.

Differential diagnosis

On mammography several other primary breast lesions may easily mimic that of a typical well-defined metastasis which may be benign or malignant:

• benign
  • fibroadenoma
• malignant
  • mucinous breast cancer
  • medullary breast cancer
  • papillary breast cancer

Rarely, metastasis to the breast may be spiculated and mimic an invasive ductal carcinoma.