LAUSR

Phyllodes tumour (PT) is a biphasic breast neoplasm that is histologically composed of a proliferation of stromal and epithelial cells. PT is characterised by a prominent and exaggerated intracanalicular growth pattern with leaf-like stromal fronds that project into stretched, arc-like epitheliallined clefts, accompanied by stromal hypercellularity. PTs are stratified into benign, borderline and malignant grades, with malignant PTs diagnosed when stromal cells exhibit marked cellularity with high-grade nuclear atypia, high mitotic activity, overgrowth and infiltrative margins. Spindle cell metaplastic breast carcinoma (SCMBC) is a morphological variant of metaplastic breast carcinoma (MBC) that is predominantly composed of spindle cells, and may have fascicular, storiform or haphazard patterns with infiltrative borders. SCMBCs are typically triple negative for oestrogen and progesterone receptors (ER and PR, respectively) and cerb-B2 (HER2). SCMBC poses a diagnostic challenge in its distinction from stroma-predominant malignant PT. The differential diagnosis of SCMBC with no morphologically recognisable epithelial differentiation from malignant PT without typical phyllodal areas is challenging, and