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.

Diffuse large B-cell lymphoma (DLBCL) may occasionally present as an intra-abdominal mass, but a dominant mesenteric root presentation can closely mimic other aggressive abdominal malignancies. Markedly elevated fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) suggests high tumor metabolic activity but is not histologically specific. A 72-year-old male presented with a two-week history of abdominal pain and was found to have a retroperitoneal mass on imaging. On physical examination, a hard, ill-defined, mobile mass was palpable above the umbilicus on deep palpation, without tenderness. Contrast-enhanced CT and FDG PET/CT demonstrated a dominant soft-tissue mass closely associated with adjacent bowel loops and mesenteric vascular structures. PET/CT showed intense FDG uptake, with a maximum standardized uptake value (SUVmax) of 35.5 on standard imaging and approximately 40.0 on delayed imaging. Preoperative imaging favored an aggressive abdominal malignancy rather than lymphoma. Because percutaneous biopsy was considered high risk due to the lesion’s location, the patient underwent surgical exploration. Intraoperative frozen-section analysis suggested a hematolymphoid malignancy, prompting the surgical team to avoid extensive bowel or mesenteric vascular resection and to limit the procedure to diagnostic tissue acquisition. Final pathology confirmed DLBCL, non-germinal center B-cell type, with a high proliferative index. This case highlights that very high FDG uptake in an abdominal mass should be interpreted as evidence of aggressive tumor biology rather than as a marker of a specific histologic diagnosis. When lymphoma is not suspected preoperatively and image-guided biopsy is unsafe, intraoperative frozen-section assessment can be critical in redirecting surgical management and avoiding non-therapeutic radical resection.