Benign spindle cell lesions of the breast: a diagnostic approach to solitary fibrous tumour, nodular pseudoangiomatous stromal hyperplasia and nodular fasciitis.

Benign spindle cell lesions of the breast include neoplastic and reactive entities that are diagnostically challenging given their rarity and similar histomorphology. Accurate diagnosis on percutaneous core biopsy within this category is essential as some lesions require excision and surveillance, whereas others may be observed. We present three cases of rare benign spindle cell lesions of the breast that reflect the diversity of this group: solitary fibrous tumour, nodular pseudoangiomatous stromal hyperplasia and nodular fasciitis. Through these cases, we discuss the associated differential diagnosis and demonstrate how emerging ancillary studies can be integrated into a diagnostic approach. We highlight distinctive clinical and histopathological features and summarise recent updates to the clinical management of these lesions. An organised approach to the broad differential of spindle cell lesions is essential for appropriate diagnosis and treatment.