Granulomatous mastitis caused by histoplasma and mimicking inflammatory breast carcinoma

Two cases of a lobular, necrotizing granulomatous process causing a unilateral painful breast mass mimicking carcinoma are presented for comparison. While the morphologic appearance in each case was that of lobular granulomatous mastitis, the etiologic agent in one case appeared to be Histoplasma capsulatum, based on Grocott methenamine silver staining, and represents the second reported case of histoplasmosis involving only breast parenchyma. Awareness of the rare entity, granulomatous mastitis, is important for the pathologist because the definitive diagnosis is made microscopically. Thorough evaluation of the breast tissue is essential for its management and should eventually contribute to the clarification of its etiology.