Xanthogranulomatous mastitis: clinicopathology and pathological implications.

Xanthogranulomatous inflammation is an uncommon finding in the breast. Sixteen cases of xanthogranulomatous mastitis were reviewed to determine the characteristic clinicopathological features. Xanthogranulomatous mastitis involved foamy histiocyte clusters interspersed with inflammatory cells. Foamy histiocytes were bland with small pyknotic nuclei. Xanthogranulomatous mastitis was associated with fat necrosis in five cases (31%), multinucleated giant-cell reactions in six cases (38%), and cholesterol crystals in five cases (31%). In three cases (19%), xanthogranulomatous mastitis coincided with ductal carcinoma in situ or invasive ductal carcinoma. Duct ectasia with foamy histiocyte aggregates were noted in five cases (31%). It is suggested that the etiology of xanthogranulomatous mastitis is obstruction and rupture of the ectatic duct with foamy histiocyte aggregates. In breast core biopsy, granular cell tumor and invasive carcinoma such as histiocytoid carcinoma and lipid-rich carcinoma could demonstrate similar pathological features to xanthogranulomatous mastitis. In conclusion, xanthogranulomatous mastitis could be encountered in breast core biopsy and surgical excision tissue. Diagnosis of xanthogranulomatous mastitis can be made by excluding other diseases that elicit xanthogranulomatous inflammation in the breast. In breast core biopsy, xanthogranulomatous mastitis could be distinguished from granular cell tumor, histiocytoid carcinoma and lipid-rich carcinoma by using cytokeratin and histiocytic marker such as alpha1-anti-trypsin and CD68 stain.