Malignant Phyllodes Tumour with Osteoclast-type Giant Cells in Young Females: A Rare Histology and Differential Diagnoses

Phyllodes tumour (PT) is a biphasic fibroepithelial tumour of the breast that accounts for 0.3-1% of all primary breast neoplasms. It is subdivided into benign, borderline, and malignant categories based on histologic features including stromal overgrowth, stromal hypercellularity, mitotic count, degree of atypia, and type of margins. Malignant PT (MPT) is characterised by infiltrative margins, marked stromal overgrowth, increased stromal hypercellularity, greater than 10 mitoses/10 high-power fields (HPFs), and moderate to severe atypia. It shows aggressive behaviour with a high risk of local recurrence and metastasis. Surgery with adequate margins is the recommended treatment. Heterologous differentiation is not an uncommon phenomenon in MPT. In addition to classic phyllodes histology, the tumour shows areas of benign/malignant mesenchymal differentiation. MPT containing multinucleated osteoclast-type giant cells (OGCs) is extremely rare. We herein report cases of MPT with OGCs in two young females who had a history of swelling in unilateral breast for two-three years. Histologic examination revealed classic phyllodes areas admixed with a sarcomatous stromal component with OGCs. Key Words: Malignant phyllodes tumour, Breast, Osteoclast-type giant cells.