Spindle cell lipoma of the breast

Spindle cell lesions, which commonly arise in the soft tissues, may present in the breast and be difficult to distinguish from primary mammary spindle cell tumors. We present the case of a 28 year old woman with a 1.5 cm circ umscribed spindle cell lipoma lying deep within the tissue of the right bre ast. Thin, uniform spindle cells were associated with collagen bundles, mat ure adipocytes and entrapped normal mammary ducts, lobules, vessels and ner ves, appearances which simulated an aggressively infiltrating tumor. The sp indle cells proved immunoreactive to CD34 and vimentin but non-reactive for cytokeratin, S100, desmin, smooth muscle actin and Factor VIII. Although s urgical resection was incomplete, the patient is alive and without evidence of tumor recurrence 12 months postoperatively, In our case, a conservative approach to management was justified and supported by the patient's subseq uent clinical course. This case exemplifies the diagnostic challenge of spindle cell lesions aris ing in breast tissue and the value of immunoperoxidase stains.