Fine-needle aspiration cytology of extra mammary metastatic lesions in the breast: A retrospective study of 36 cases diagnosed during 18 years

Background: Metastatic tumors in the breast require treatment according to origin and type of tumor. It is important to recognize these lesions in fine-needle aspiration cytology (FNAC) in order to avoid unnecessary mastectomy or non-relevant chemotherapy. The aim of this study was to evaluate the cytological features of metastatic tumors and possible criteria that could alert us as to the possibility of a metastasis from an extra mammary malignancy. Methods: The material included 36 confirmed or suspected metastases in the breast registered in the pathology files at Oslo University Hospital, Ulleval, during 1990–2007. There were a total of 6,325 cases of malignant breast FNAC, representing 30 men and 6,295 women. Smears were evaluated for the amount of material, presence or absence of myoepithelial cells, microcalcifications, mitoses and necrotic material. All carcinomas were graded. Results: There were seven men (7/30 = 23.3%) and 29 women (29/6,295 = 0.46%). The primary tumor was known in 22 cases (22/36 = 61.1%). No other primary tumor was known and metastatic lesion was not initially suspected in 14 cases (14/36 = 38.9%). The most common origin was lung (15/36 = 41.7%). In five cases (5/36 = 13.9%), the origin remained uncertain. Conclusions: Metastases from extra mammary sites are (relatively) common in males (23.3%). In women, metastatic lesions are rare (0.46%). A large proportion of them (88%) are high-grade adenocarcinomas and poorly differentiated carcinomas that may resemble grade 3 ductal carcinomas. Unusual clinical and/or radiological presentation in combination with high-grade malignant cells should alert us to consider the possibility of a metastasis.