Cutaneous/subcutaneous mesenchymal proliferations of the breast

Cutaneous mesenchymal “spindle cell” lesions arising in the vicinity of the breast represent a complex clinical and diagnostic scenario which may overlap histopathologically and immunohistochemically with mammary spindle cell proliferations, potentially impacting management and overall prognostication. In this review, we suggest a pattern-based approach to assist in the evaluation of these lesions. A comprehensive description of each entity is accompanied by a cutaneous and mammary differential diagnosis.