Background: The presence of highly cellular stromal fragments in breast fine needle aspirates (FNA) suggests some classical differential diagnoses such as cellular fibroadenoma, phyllodes tumour (PT), metaplastic carcinomas, and some mesenchymal/myoepithelial proliferations. The other components of the smears can help in the differential diagnosis, but the presence of a low-grade epithelial proliferation does not always represent a fibro-epithelial lesion as we demonstrate in these two cases. Cases: We discuss two cases of breast FNA, previously presented in a slide seminar at the 29th European Congress of Pathology in Amsterdam, where the common cytological finding was the presence of stromal cellular fragments together with an epithelial component. One case is a typical PT and the other is a case of a mammary carcinoma with osteoclast-like giant cells. Conclusion: Mammary carcinoma with osteoclast-like giant cells is an unusual type of breast carcinoma that should be included in the differential diagnosis of breast lesions containing cellular stroma. Since the associated carcinoma is usually low grade, careful evaluation for malignant cells on cytological smears is necessary for an accurate differential diagnosis with PT where the epithelial component is benign.

Keywords:
Breast fine needle aspirates, Phyllodes tumour, Fibroadenoma, Cellular stroma, Mammary carcinoma with osteoclast-like giant cells
© 2018 S. Karger AG, Basel
2018
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