This book utilizes a uniform approach to provide a framework for the diagnosis of mesenchymal tumors of the breast while highlighting their mimics. Emphasis is placed on a practical approach to the morphologic interpretation and useful ancillary tests while exploring the differential diagnoses in depth. Given the overall low incidence of mesenchymal lesions of the breast along with their mimics, surgical pathologists are not consistently exposed to these spindle cell lesions. Compounding this problem is the broad differential that these lesions engender, with entities ranging from reactive/reparative lesions to poorly differentiated spindle cell malignancies. Furthering the challenge, the diagnoses may be complicated by fixation issues, sampling method, small sample size, lack of clinical history and prior treatment effects. The goal of this book is to introduce readers to the spectrum of these lesions while providing a systematic approach that helps establish accurate diagnoses that in turn drive appropriate clinical follow up and treatment. Chapters cover the spectrum of benign and malignant mesenchymal tumors and their mimics that are found in the breast in an easy to read format with richly detailed images to aid in diagnoses. The text also discusses practical components to aid in establishing and evaluating the differential diagnosis. Given how morphologically and clinically diverse these lesions are, Mesenchymal Tumors of the Breast and Their Mimics provides a construct for integrating the varied components that go into establishing a diagnosis for this challenging aspect of breast pathology.