Spindle cell lesions in the breast encompass a heterogeneous group of lesions, including reactive processes, and benign and malignant neoplasms. Management and prognosis vary substantially according to the diagnosis. However, differentiating between these lesions can be difficult, especially when only limited biopsy samples are available. In this article, we highlight the main spindle cell lesions encountered in the breast, including microscopic findings, immunohistochemistry profile, molecular findings, and pitfalls.