• Ruinuan Wu, Xikang Wu, Xin Weng, Yingjie Xiu, Gang Xu, Xiajing Liu, and Xia Liu.
• Department of Pathology, Shenzhen Second People's Hospital, Shenzhen, China.
• Medicine (Baltimore). 2023 Feb 17; 102 (7): e32995e32995.

RationaleGiant cell tumor of bone is a locally aggressive and rarely metastasizing neoplasm that typically affects the ends of long bones or the axial skeleton of young to middle-aged adults. As many as 69% to 100% of giant cell tumors harbor H3F3A gene mutations, while H3F3B gene mutations have rarely been reported.Patient ConcernsA 53-year-old male patient who underwent right distal femoral tumor resection.DiagnosesPreoperative CT plain scan indicated giant cell tumor of bone with pathological fracture. Laboratory findings were as follows: serum calcium was 2.23 mmol/L (reference range: 2.1-2.55 mmol/L) and serum phosphorus was 1.35 mmol/L (reference range: 0.81-1.45 mmol/L).InterventionsThe histological morphology showed the typical features of a conventional GCT. The immunoprecipitation analysis results were as follows: H3.3G34W(-), H3.3G34R(-), H3.3G34V(-), and H3K36M(-). Sanger sequencing showed that the H3F3A and H3F3B gene mutations were wild type. The high-throughput gene sequencing results revealed the H3F3B gene mutations H3.3p.Gly35Trp and H3.3p.Val36Leu.OutcomesThe patient was stable with no recurrence in 12 months follow-up.LessonsGiant cell tumor of bone with H3F3B gene mutations is extremely rare. In the pathological diagnosis of bone tumors, we need to analyze clinical presentation, imaging features, histology, immunophenotype, and cytogenetic/molecular alterations, in order to get a correct diagnosis.Copyright © 2023 the Author(s). Published by Wolters Kluwer Health, Inc.

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