CD10, a Useful Marker for Atypical Fibroxanthomas

To the Editor: CD10, a cell-surface neutral endopeptidase, is expressed by lymphoid precursor cells, B-lymphoid cells of germinal center origin, and tumors derived from them. More recently, it has been described in a large number of normal tissues and tumors such as renal glomerular and tubular cells, renal cell carcinomas, salivary gland and breast myoepithelial cells, endometrial stroma, and various mesonephric and trophoblastic tumors.1,2 We wish to add another tumor type to this expanding list. Perhaps CD10 will become ‘the vimentin of the 21st century’! The ‘discovery’ was made serendipitously during the work-up of a CD10-positive clear cell tumor of the skin. One of us (DW), on seeing the lesion, in consultation, diagnosed atypical fibroxanthoma of the rare clear cell type. As a consequence, we randomly selected 20 paraffin blocks (that had already been retrieved for a study of the outcome of 100 atypical fibroxanthomas) of previously diagnosed cases and performed staining for CD10. All 20 cases were positive. Since that finding more than 6 months ago, we have added CD10 to our routine panel for bizarre spindle cell tumors of the skin and soft tissues. Approximately 30 such cases have been studied. CD10 has been expressed in all 3 malignant fibrous histiocytomas encountered. It was not expressed in one presumptive case of atypical fibroxanthomas (AFX), but it has been in another 10 cases. We have encountered 2 tumors that expressed both CD10 (60-80% of cells) and the broad keratin marker MNF116 (approximately 20% of the tumor cells). We are uncertain as to the histogenesis of such cases, although Zelger and Soyer have previously expressed the view that atypical fibroxanthomas are nothing more than variants of squamous cell carcinoma.3 This view does not seem to be supported by our detailed study of atypical fibroxanthoma, mentioned above.4 David Weedon, MD, FRCPA Richard Williamson, MBBS, FRCPA Basit Mirza, MBBS Sullivan Nicolaides Pathology Taringa, Qld. Australia, Department of Dermatology Greenslopes Private Hospital Brisbane, Qld. Australia