Extensive squamous metaplasia in gynecomastia

Extensive squamous metaplasia is described in a case of gynecomastia. Numerous ducts in all sections of breast tissue revealed multiple foci of squamous metaplasia, many of which included large, papillary excrescences of keratinizing squamous cells into duct lumens, with foci of dyskeratosis. Review of four years of gynecomastia cases from our surgical pathology files revealed a total incidence of squamous metaplasia equaling six of 40 cases of gynecomastia, including the case reported here. The other five cases included only one or two small foci of squamous metaplasia. These findings demonstrate that squamous metaplasia in gynecomastia is not rare, but is usually very limited. However, an unusual case, such as that reported here, may show extensive, florid squamous metaplasia, without associated inflammation or neoplasm.