Microscopic description and IHC:

The H&E slide shows cores of breast tissue infiltrated by a malignant appearing lesion with micropapillary features. The cells are arranged in knot-like nests and exhibit areas of cribriforming. The cells have small uniform nuclei with only mild variation in size and a low mitotic count, consistent with a low grade serous carcinoma. Psammoma bodies are not seen in this case. The lesion strongly expressed PAX8, and did not express GATA3, further supporting an ovarian origin.

Discussion:

Knowing this patients history of a malignant ovarian neoplasm is crucial in this case. Breast metastases from an ovarian primary tumor is exceedingly rare.

Without the patient’s history, it would be difficult to distinguish this case from invasive micropapillary carcinoma of the breast, which is a very rare entity in and of itself. One helpful discriminating feature would be the presence of ductal carcinoma in situ (DCIS) seen associated with the micropapillary carcinoma, which would of course make it much more likely that this was a primary breast lesion. Micropapillary carcinoma of the breast is commonly ER and PR positive. About one third of cases overexpress HER2. These additional immunohistochemical markers may also be useful in some cases.

Adenoid cystic carcinoma of the breast is another rare breast carcinoma. It has an excellent prognosis. Most patients are in their sixth or seventh decade at the age of diagnosis, unlike the patient in this case, who is in her thirties. Histologically, they closely resemble adenoid cystic carcinomas of the salivary gland and are often CD177 (ckit) positive. One may be able to argue the presence of tubule formation, in favor of invasive ductal carcinoma of the breast, however the immunohistochemistry and micropapillary features more strongly favor metastatic serous carcinoma.

References:

Mhawech-Fauceglia P, Kay B, Li CJ, Lin YG. Metastatic ovarian papillary serous carcinoma to the breast: Diagnosis and pitfalls. Gynecologic Oncology Reports 4 (2013) 35–37.

Nonaka, D., Chiriboga, L., Soslow, R.A., 2008. Expression of PAX8 as a useful marker in distinguishing ovarian carcinomas from mammary carcinomas. Am. J. Surg. Pathol. 32, 1566–1571.

Schnitt SJ, Collins LC. Biopsy Interpretation of the Breast. 2nd edn. Lippincott Williams & Wilkins: Philadelphia; 2001.

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