Metastatic neoplasms of the breast are very rare 12. They may mimic benign and malignant primary neoplasms both clinically and radiologically 3, and the clinical diagnosis often goes unsuspected, especially when the first manifestation of the clinical picture is a breast tumor and the existence of a primary neoplasm is unknown or not taken into consideration 4. In most cases, management through fine needle aspiration biopsy (FNAB) permits the correct diagnosis of a metastatic neoplasm, which prevents unnecessary radical surgeries and allows us to start appropriate systemic treatment promptly 5.

For FNAB evaluation it is necessary to know the patient's clinical history. It will usually be easier to achieve a definitive diagnosis when the history of extramammary malignant neoplasm is known. Therefore, metastatic lesions should be considered in the differential diagnosis of tumors of the breast, particularly in those cases presenting unusual clinical, radiological, or cytological characteristics. For the latter, it is very useful to perform immunocytochemistry stains on the smears or cell blocks to arrive at a definitive diagnosis.

Three cases of metastatic neoplasms of the breast were identified through FNAB, from a total 639 aspirates of breast tumors performed between January 2001 and December 2003 at the Aspiration Room of the Anatomical Pathology and Cytopathology Service of the Hospital Universitario. The pathologist performed all the procedures by using a gauge 22 needle in a 10 ml syringe. One or two punctures were performed in each case, with an average of four smears per patient. An air-dried smear was stained with Diff-Quik for immediate evaluation of the sample, and the rest were fixed with 95° alcohol and stained by Papanicolau's method. Additionally, immunohistochemistry stains were performed on the cytological material [Table 1].

Out of a total 639 aspiration biopsies of the breast, 3 cases (0.4%) were diagnosed as metastatic neoplasms. In the three cases, immunochemistry was performed on the smears to corroborate the diagnosis, and the histological slides of the primary tumor were reviewed in order to compare them with the original morphology.

Metastases to the breast of neoplasms originating in organs other than the breast are very rare. In a series of 2529 breast aspiration biopsies, 666 were diagnosed as malignant neoplasms, and only 18 (2.7%) were of extramammary origin 5. The identification of a secondary neoplasm in the breast is clinically complicated because secondary neoplasms appear as well-circumscribed rounded masses, most often located in the upper outer quadrant, and without the spiculations or microcalcifications of primary carcinomas 6. On the other hand, the presence of well-circumscribed multiple or bilateral nodules may suggest a benign process in the mammography 7.

Since metastatic neoplasms may mimic primary tumors, it is important to know the patient's clinical history when interpreting the FNAB. However, for patients with unknown primary neoplasms the metastatic nature of the lesion should be suspected when we find unusual cytological patterns. Immunocytochemistry techniques are undoubtedly of great use in the latter cases.

Some clinical characteristics help us identify neoplasms of the breast that have a metastatic origin: the time span for the development of metastasis in patients with previously treated cancers is approximately two years. Metastases are usually to other sites or are detected simultaneously; by contrast, isolated metastases limited to the breast are infrequent 8.

Although virtually any malignant neoplasm can metastasize to the breast, this is most common for melanomas, carcinomas of the lung, neuroendrocrine and carcinoid carcinomas, ovarian carcinomas, and lymphoid and hematopoietic neoplasms 5891011. Extracranial metastases of medulloblastoma occur in 5% to 7% of cases, and they are mainly related to ventricular peritoneal shunts. Most frequently affected sites are the bones, the lymphatic nodes, the liver, and the lungs, with isolated cases reported for other organs, such as the breast, for which only five cases have been described in the literature. Three of these cases were diagnosed through fine needle aspiration biopsy 1213141516.

The cytological differential diagnosis includes lobular carcinoma, small-cell carcinoma, carcinoid tumor, lymphoma, and leukemic infiltration. Melanomas are some of the neoplasms that most often metastasize to the breast. Such metastases may be hard to recognize if the primary tumor is hiding or if there is no history of this tumor 1718.

In addition, there is only one reported case of granulosa cell ovarian tumor metastatic to the breast diagnosed through a biopsy 19, and there are no previous reports of cases diagnosed with FNAB.

Metastatic disease should be taken into consideration in the differential diagnosis of a tumor of the breast, especially if there is a history of an extramammary malignant neoplasm. FNAB, in combination with Immunohistochemistry, is the method of choice for the initial management of these cases. On the other hand, comparing the cytological findings with the previous biopsy will be usually enough to arrive at a correct diagnosis, thus preventing unnecessary radical surgical procedures and allowing us to establish the treatment of choice promptly and safely.