Calcifying fibrous pseudotumor.

A case of calcifying fibrous pseudotumor arising in the ingune of a 20-year-old Japanese female is described. The patient had a well-circumscribed subcutaneous mass measuring 2.0 cm in greatest diameter, which had been present for 3 months. Microscopically, the tumor was not encapsulated but well defined. The tumor was composed largely of dense interwoven bundles of collagen. Uniform, elongated spindle cells were scattered among the collagenous bundles and showed a wavy pattern. Lymphoid follicles with germinal centers and an infiltration of lymphocytes and plasma cells were intermingled. The tumor was characterized by the presence of microcalcifications, chiefly dystrophic calcifications, throughout the lesion. The spindle cells were diffusely positive for vimentin and alpha-smooth muscle actin. They were uniformly negative for desmin, muscle specific actin HHF35, factor-VIII related antigen, S-100 protein, neurofilament, cytokeratin CAM5.2, CD34, and CD31. By flow cytometry the tumor had a diploid DNA content with S-phase fractions of 2.5%. The patient was well with no evidence of disease 2 months after excision.