Wide spectrum screening keratin as a marker of metaplastic spindle cell carcinoma of the breast: an immunohistochemical study of 24 patients

Aims: Metaplastic spindle cell carcinomas may be difficult to distinguish histologically from other spindle cell lesions in the breast. Variable staining with cytokeratin immunomarkers has been reported for metaplastic carcinomas. We evaluated the diagnostic utility of anti-cytokeratin polyclonal antibody, wide spectrum screening keratin, to assess spindle cell breast lesions. Methods and results: Twenty-four patients with spindle cell breast carcinoma and 31 patients with benign or malignant spindle cell tumours were studied using a panel of antibodies directed against multiple cytokeratins (AE1/AE3, CAM5.2, wide spectrum screening keratin), epithelial membrane antigen (EMA), and vimentin. Sites of origin for the 31 controls included breast, bone, and soft tissue. All but one (95.8%) metaplastic carcinomas stained positively with wide spectrum screening keratin. Only rare or focal immunoreactivity was observed with AE1/AE3 in four cases; however, sensitivity of AE1/AE3 was improved in 13 cases using steam EDTA as an antigen retrieval technique. Three cases were immunoreactive with CAM5.2 and eight cases were immunoreactive with EMA. All control cases lacked immunoreactivity with the cytokeratin panel and EMA. The spindle cells in the metaplastic breast tumours (88%) and in the controls (97%) stained with vimentin. Conclusions: Wide spectrum screening keratin may be the most useful and convenient antibody in differentiating metaplastic spindle cell carcinoma from other spindle cell lesions in the breast.