Dermatofibrosarcoma protuberans: ultrastructural investigation. 
The ultrastructural aspects of nucleus and cytoplasm of tumor cells and the interstitial material of dermatofibrosarcoma protuberans are described in detail, especially the very peculiar labyrinthic nucleus.  Opinions about its development are reviewed; some, such as melanocytic, neural, histiocytic and smooth muscle proliferation, might be discarded.  The myofibroblast appears as the most probable stem cell.