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 circumscribed spindle cell lipoma lying deep within the tissue of the right breast. Thin, uniform spindle cells were associated with collagen bundles, mature adipocytes and entrapped normal mammary ducts, lobules, vessels and nerves, appearances which simulated an aggressively infiltrating tumor. The spindle cells proved immunoreactive to CD34 and vimentin but non-reactive for cytokeratin, S100, desmin, smooth muscle actin and Factor VIII. Although surgical 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 subsequent clinical course. This case exemplifies the diagnostic challenge of spindle cell lesions arising in breast tissue and the value of immunoperoxidase stains.