Clinicopathological and genetic findings of infantile nodular fasciitis

To the Editor:Nodular fasciitis(NF)has been described as a rapidly growing benign soft tissue tumor with fibroblas-tic/myofibroblastic proliferation.[1]It commonly involves the upper extremities of adults aged 20 to 40 years.[1]Due to its rapid growth rate,high cellularity,and brisk mitosis,these lesions are easily confused with soft tissue sarcomas in the diagnosis-making process.Recent findings indicated that recurrent gene rearrangement of ubiquitin-specific protease 6(USP6),located at 17p13.2,favors the clonally proliferative nature of NF.[1]USP6 rearrangements have been discovered in approximately 90%of NF cases and>65%of NFs harbor myosin heavy chain 9(MYH9)-USP6 fusions with a type I(exon 1–exon 1)or type II(exon 1–exon 2)pattern.[1,2]Thus,USP6 rearrangements have been adopted as a valuable diagnostic biomarker for distinguishing challenging cases from their histologic mimics.NF is frequently seen in adulthood but extremely rare in infants.Here,we evaluated the clinical,pathologi-cal,and genetic features of infantile NF to understand the tumorigenesis mechanism underlying this entity.