Case Number : Case 2149 - 4 September 2018 Posted By: Uma Sundram

Myxoid DFSP

myxoid DFSP

DFSP

Mmh...spindle cells intermingled with sclerotic collagen bands are typical of dermatofibroma. This trapping is usually in the lateral and deep margins of the lesion, unlike what you can see in this case, where the trapping is widespread. At high magnification the neoplastic cells look like histiocytic or lipidized. So, without CD34 positivity, my first spot is DF.

Thank you for your comments. A very difficult case. In fact, this was called DFSP based on focal, central CD34 positivity. However, there was 1) only focal fat entrapment, as Vincenzo has pointed out and 2) cytologic atypia, unusual in DFSP (although not in DFSP with fibrosarcomatous transformation).  Lipidized cells/histiocytoid cells are also unusual for DFSP. In the panel with reticular dermis, you can see fat trapping is fairly superficial; in DFSP, the lesion itself is centered on fat. The atypia and presence of histiocytic cells led us to favor atypical fibrous histiocytoma/superficial pleomorphic undifferentiated sarcoma. The lesion was small and easily re excised; the designation of superficial pleomorphic US allows for more close follow up.

You may also note in this case, that the spindled cells are short with ample cytoplasm; in DFSP, one usually sees less cytoplasm. Also, in DFSP-FS, a herringbone pattern typical of FS is usually seen, which was missing in this case. One of the last panels demonstrates good collagen trapping, typical of fibrous histiocytomas.

Atypical DF in ddx.

Agree, atypical DF is a consideration. These are also known as atypical fibrous histiocytoma in the literature. The terminology is confusing!