Breast, Synovial-type Metaplasia

The presence of a foreign body can result in reactive changes within the surrounding connective tissue. One such reaction is synovial-type metaplasia, in which the tissue in contact with a breast expander or implant transforms into a lining similar to a joint space. Rarely, it can be florid as in this case. The cells are similar immunohistochemically to true synovial cells (CD68 positive, cytokeratin negative).