LN-2 (CD74) - A MARKER TO DISTINGUISH ATYPICAL FIBROXANTHOMA FROM MALIGNANT FIBROUS HISTIOCYTOMA

BACKGROUND. In this study, the authors examined the expression of LN-2 , an antigen expressed by B cells, macrophages, and Reed-Sternberg cel ls, in a variety of spindle cell lesions of the skin to determine whet her LN-2 immunoreactivity can be used to differentiate among these tum ors. For comparison, they examined CD34 antigen expression in these le sions, which has been shown to be a useful marker in differentiating d ermatofibrosarcoma protuberans from dermatofibroma. METHODS. Immunocyt ochemistry with anti-LN-2 and anti-CD34 monoclonal antibodies on forma lin fixed, paraffin embedded material was performed on 102 spindle cel l lesions, including dermatofibroma, dermatofibrosarcoma protuberans, atypical fibroxanthoma, malignant fibrous histiocytoma, leiomyoma, and neurofibroma.RESULTS. LN-2 immunoreactivity did not distinguish betwe en dermatofibroma and dermatofibrosarcoma protuberans, both of which s howed weak immunoreactivity. In marked contrast, 90% of cases of malig nant fibrous histiocytoma showed strong staining for LN-2, whereas the vast majority (90%) of cases of atypical fibroxanthoma were negative or stained only weakly with anti-LN-2 antibodies. Of the two cases of atypical fibroxanthoma that stained strongly for LN-2, both lesions we re >2 cm in size and extended deep into the subcutaneous fat. CONCLUSI ONS. Differential expression of the LN-2 antigen by atypical fibroxant homa and malignant fibrous histiocytoma distinguishes these two lesion s and suggests that acquisition of LN-2 positivity may be a marker of tumor progression. (C) 1997 American Cancer Society.