Low‐grade fibromyxoid sarcoma versus fibromatosis: A comparative study of clinicopathological and immunohistochemical features

We have studied 11 cases of low-grade fibromyxoid sarcoma (LGFMS) and 15 cases of fibromatosis with respect to clinicopathological features and immunohistochemical expression of Ki-67, nm23, cyclinD1, and p53, in order to investigate the differential diagnosis between this two groups. Formalin-fixed, paraffin-embedded sections from 11 cases of LGFMS and 15 cases of fibromatosis were studied histologically and immunohistochemically. The immunostainings were semiquantitatively evaluated using the Allred score system. Microscopically, LGFMS was composed of bland spindle cells arranged in a whorled pattern showing alternating myxoid zones and fibrous stroma zones with prominent arcade curvilinear capillaries. Cytological atypia, mitotic figures, and tumor necrosis were absent in all 11 cases of LGFMS. In contrast, fibromatosis was less cellular and more fascicular, containing more collagen and showing no alternating fibrous and myxoid zones as compared with LGFMS. The immunostaining scores of nm23 in LGFMS were significantly lower than that in fibromatosis. The immunostaining scores of Ki-67, p53, and cyclinD1 in LGFMS were significantly higher than that in fibromatosis. Thus, we consider that LGFMS can be distinguished from fibromatosis by clinicopathological features, and assessments of the immunohistochemical expression level of cyclinD1, p53, nm23, and Ki-67 are helpful in the differential diagnosis.