LN‐2 (CD74)

BACKGROUND In this study, the authors examined the expression of LN‐2, an antigen expressed by B cells, macrophages, and Reed‐Sternberg cells, in a variety of spindle cell lesions of the skin to determine whether LN‐2 immunoreactivity can be used to differentiate among these tumors. For comparison, they examined CD34 antigen expression in these lesions, which has been shown to be a useful marker in differentiating dermatofibrosarcoma protuberans from dermatofibroma. METHODS Immunocytochemistry with anti‐LN‐2 and anti‐CD34 monoclonal antibodies on formalin fixed, paraffin embedded material was performed on 102 spindle cell lesions, including dermatofibroma, dermatofibrosarcoma protuberans, atypical fibroxanthoma, malignant fibrous histiocytoma, leiomyoma, and neurofibroma. RESULTS LN‐2 immunoreactivity did not distinguish between dermatofibroma and dermatofibrosarcoma protuberans, both of which showed weak immunoreactivity. In marked contrast, 90% of cases of malignant 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 were >2 cm in size and extended deep into the subcutaneous fat. CONCLUSIONS Differential expression of the LN‐2 antigen by atypical fibroxanthoma and malignant fibrous histiocytoma distinguishes these two lesions and suggests that acquisition of LN‐2 positivity may be a marker of tumor progression. Cancer 1997; 79:2115‐24. © 1997 American Cancer Society.