Fine needle aspiration cytology of mammary carcinoma with osteoclast-like giant cells

Carcinoma with osteoclast-like giant cells (OCGC) is an uncommon neoplasm characterized by giant cells, prominent vascularization, haemorrhage and areas of cribriform epithelial growth with moderate atypia. Multinucleated giant cells (MGC) have been described in several other breast lesions raising an interesting differential diagnosis, mainly with benign disorders. Due to its rarity few cases have been described cytologically. We retrospectively reviewed 13 fine needle aspiration samples from nine patients with this variant of carcinoma. Nine corresponded to breast tumours and four to axillary, liver, subcutaneous and mediastinal metastatic lesions. The expression of CD68 by giant cells was evaluated immunocytochemically in six cases. All patients had a complete pathological study of the breast neoplasm. Smears showed a double component of epithelial and giant cells. Epithelial clusters were predominantly of intermediate size with irregular contours. Most were cohesive but others showed cellular dissociation with scarce to moderate cellular pleomorphism. Giant cells had well defined, deeply stained cytoplasm and round to elongated morphology. Two metastatic cases were devoid of them. Haemosiderin-laden macrophages were common in smears from breast tumours. In the six cases tested CD68 was expressed in MGC. Cytological features of mammary carcinoma with OCGC correlate closely with the histological ones. Most cases are clearly recognizable as malignant but in others cytological atypia may be minimal, mimicking a benign lesion. In difficult cases the presence of haemosiderin-laden macrophages and the histiocytic nature of the MGC are helpful diagnostic features.