Teaching Case

A 43-year-old female patient complained about recent right breast tenderness and enlargement.
Three months before she had been diagnosed with a locally advanced gastric carcinoma, already with peritoneal implants.

The mammograms show breasts with heterogeneously dense tissue composition.
In the right breast, a large predominantly radiopaque focal asymmetry was seen high in the transition between the upper quadrants, assuming an almost encapsulated presentation with mixed density.
There were neither obvious distortions, nor suspicious calcifications.

An ultrasound was made for further characterization of the area of concern and revealed a poorly defined hypoechoic rim surrounding a more echogenic area with apparently preserved glandular tissue, lacking an obvious encapsulation, but measuring about 30 mm. The remaining breast tissue did not show any suspicious nodules or cysts. No axillary adenopathy was found.

The findings suggested a benign hamartoma, but we decided to make a core biopsy in the area as the patient came back 3 months later, with increasing local complains.

The samples taken revealed histological and immunohistochemical features consistent with gastric carcinoma infiltrating the breast tissue.

Metastasis to the breast can occur by two routes, a cross-lymphatic route, most commonly from a contra-lateral primary breast malignancy, and blood-borne metastasis from extra-mammary malignancies. [1]

The distinction between primary breast cancers and metastases from extra-mammary malignancies is critical for the patient, as the latter option is often associated with a widely disseminated disease that portends a dismal prognosis. [2]

Besides gastric adenocarcinomas, the literature states a wide range of extra-mammary tumours metastasizing to the breast, the largest group being haematological malignancies. Other common primaries are lung carcinoma, malignant melanoma, serous papillary carcinoma of the ovary, prostate carcinoma, kidney and carcinoid tumours. [1, 2, 3]

Metastases to the breast may be single or multiple and tend to be superficial and located in the upper outer quadrant when haematogenously spread [2]. These lesions usually manifest as round or oval masses on mammography, with partially circumscribed or fading margins. Calcifications are unusual, except for rare instances of metastasis from ovarian, thyroid, or mucin-producing gastrointestinal tract carcinomas [1].
Skin and nipple retractions are usually absent, as little desmoplasia is associated with these lesions [1, 2, 3].

Ultrasound often reveals hypoechoic solid lesions, with distinct or poorly defined margins.
Axillary lymphadenopathies are less common in metastases than in primary breast cancers but can also present in patients with metastasis spread by the lymphatic route [2].

As take home points, we conclude that breast metastases from extra-mammary malignancies show variable imaging features. Therefore, this differential diagnosis should be considered when evaluating breast lesions in patients with a known primary malignancy in other organs. Awareness of the most common imaging features may be helpful to guide to the right diagnosis.