Coexistence of spindle cell lipoma and ordinary lipoma.

We report a patient with a spindle cell lipoma on the nape and three ordinary lipomas on the abdomen and extremities. The coexistence of spindle cell lipoma and ordinary lipoma in a single patient is rare. Abundant CD34-positive spindle cells and mast cells were found in the spindle cell lipoma, but in the ordinary lipomas, only a small number of CD34-positive spindle cells were found in the interstitial connective tissue and no mast cells were seen. Because mast cells are known to stimulate mesenchymal cell proliferation and collagen production, mast cell infiltration may be a trigger for the proliferation of CD34-positive spindle cells, leading to the conversion of ordinary lipoma into spindle cell lipoma.