Diffusely scattered calcifications visible with mammography are almost always benign. Certain patterns, however, should arouse concern. For example, extensive comedocarcinoma is associated with large areas of mammographically visible calcium deposition. The authors identified 10 women in whom calcifications were visible throughout large volumes of breast tissue at mammography. The calcifications did not resemble those typical of extensive comedocarcinoma, yet they were associated with extensive breast cancer. Their mammographic pattern was characterized by a strikingly wild, chaotic appearance with profuse deposition of calcium. As in many cancers, the particles were heterogeneous, but unlike in most carcinomas, many deposits had a typically benign morphology. Histologic examination showed that even these typically benign calcifications were associated with malignant cells. The authors believe that the apocrine features displayed by many of the cancer cells in these 10 patients may explain the unusual profusion of calcium deposits.