Pseudosarcomatous Fasciitis of the Breast Simulating a Malignant Neoplasm: A Case Report and Ultrastructural Study

A rare case of pseudosarcomatous fasciitis of the breast simulatingbreast cancer in clinical and gross features was studied bylight and electron microscopy. The pseudo-tumor was located in the right breast of a 59-year-oldJapanese woman, who underwent a radical mastectomy. The tumorcells were mainly composed of fibroblast-like cells within fibrousstroma and appeared to infiltrate into the subcutaneous fattytissue. Normal or atrophic lobules and ductules of the mammarygland were also found with occasional microcalcification. The ultrastructure of the tumor cells showed poorly developedrough endo-plasmic reticula, and abundant intracytoplasmic microfilaments.This finding suggests that the pseudotumor cells were proliferativefibroblasts derived from the superficial fascia of the breast.