[A case report: retroperitoneal inflammatory fibrosarcoma that revealed progressive enlargement].

A 65-year-old woman presented with microscopic hematuria. Computed tomography (CT) and magnetic resonance imaging revealed a solid tumor measuring 64 x 55 x 71 mm adjacent to the right kidney. After 51 days, the CT demonstrated progressive enlargement of the tumor (110 x 80 x 82 mm), and the tumor-doubling time was calculated as 33 days. A transperitoneal right radical nephrectomy was performed. Histologically, the tumor was arising from retroperitoneum and consisted of variable arranged spindle cell proliferation with an infiltration of inflammatory cells. Immunostaining examination showed positive staining for alpha-smooth muscle actin (SMA), vimentin, cytokeatins, and CD 68, whereas desmin, CD 34, and p53 were negative. High proliferative activity (20%) was demonstrated by MIB1 immunostaining. Then the tumor was diagnosed as inflammatory fibrosarcoma. The patient has been followed up for 3 months since the operation with no evidence of local recurrence or distant metastasis.