Lipofibromatosis: a clinicopathological analysis of eight cases

Abstract

Objective: To investigate the clinicopathological characteristics and differential diagnosis of lipofibromatosis. Methods: The clinicopathological features and immunohistochemical profiles in 8 cases of lipofibromatosis diagnosed at Fudan University Shanghai Cancer Center from January 2008 to June 2017 were studied. Molecular analysis of β-catenin mutation by Sanger sequencing, NTKR1 and ETV6 rearrangements by FISH were performed. The follow up information was evaluated and the literature was reviewed. Results: There were 4 males and 4 females with a median age of 1.5 years at presentation (range, 3 months-9 years). Tumor arose in the hand (4 cases), foot (2 cases) and trunk (2 cases), manifesting as a painless subcutaneous mass. Two cases were congenital, one with tumor noted at birth and the others shortly after birth. Grossly, the tumors were poorly defined and irregularly shaped, composed predominantly of fatty tissue which was mingled with fibrous element. They ranged from 1 to 5 cm in size (mean, 2.6 cm). Microscopically, they were characterized by variably sized lobules of adipose tissue traversed by fascicles, bundles or trabeculae of proliferative fibroblasts and myofibroblasts, resembling desmoid tumor. In 2 cases, the tumor infiltrated adjacent skeletal muscles. On high power, the spindled fibroblasts and myofibroblasts had a bland appearance with very low mitotic activity (<1/10 HPF). By immunohistochemistry, they showed variable staining of α-SMA, MSA, CD34 and CD99, with negativity for β-catenin, desmin, h-CALD, EMA, ALK, and S-100 protein. Ki-67 index was low (<2%). Molecular analysis showed no mutation of β-catenin gene (0/3), no NTRK1 gene rearrangement (0/3) and no ETV6 gene rearrangement (0/2). Follow up information was available in 6 patients, revealed local recurrence in two and persistent disease in one. Conclusions: Lipofibromatosis is a special variant of infantile fibromatosis, which has a predilection for the distal portion of the extremities of neonates and infants and characterized by lobules of adipose tissue traversed by demoid tumor-like fibroblasts and myofibroblasts. However, it differs from desmoid tumor by harboring no mutation of β-catenin gene. Familarity with its clinicopathological characteristics helps the distinction from its morphological mimics.