Identification of EML4-ALK as an alternative fusion gene in epithelioid inflammatory myofibroblastic sarcoma

Quan Jiang, Han-Xing Tong, Ying-Yong Hou, Yong Zhang, Jing-Lei Li, Yu-Hong Zhou, Jing Xu, Jiong-Yuan Wang, Wei-Qi Lu

Known as solid tumors of intermediate malignant potential, most inflammatory myofibroblastic tumors (IMTs) are treatable as long as the tumor is en-bloc resected. However, in some cases, the tumors have recurred and grown rapidly after successful surgery. Some of these tumors were classified as an epithelioid inflammatory myofibroblastic sarcoma (EIMS). Most previously reported EIMSs have been caused by RANBP2-ALK fusion gene. We herein report an EIMS case caused by an EML4-ALK fusion gene. RNAseq was conducted to find out the new ALK fusion gene which could not be detected following previously reported RT-PCR methods for EIMS cases with RANBP2-ALK fusion gene. After that, RT-PCR was also conducted to further prove the newly found fusion gene. Immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) test were applied to find out the unique morphological characters compared with the previous reported EIMS cases. We found an EIMS case who was suffering from a rapid recurrence after cytoreducyive surgery was done to relieve the exacerbating symptoms. The patient finally died for tumor lysis syndrome after the application of crizotinib. Distinctive ALK staining under the membrane and relatively weak ALK staining in the cytoplasm could also be observed. RNAseq and RT-PCR further revealed that the tumor harbored an EML4-ALK fusion gene. In conclusion, this is the first EIMS demonstrated to have been caused by the formation of an EML4-ALK fusion gene. This enriches the spectrum of EIMS and enlarges the horizon for the study of EIMS. The experience we shared in managing this kind of disease by discussing aspects of its success and failure could be of great value for surgeons and pathologists.