Uterine leiomyoma-like inflammatory myofibroblastic tumour with a rare ALK::SYN3 fusion: a clinicopathologic and molecular analysis.

Uterine inflammatory myofibroblastic tumour (IMT) is a relatively rare mesenchymal tumour of the uterus, with recurrence and metastasis rates of 25% and 2%, respectively. As IMT frequently harbours ALK gene rearrangements, some patients may benefit from treatment with tyrosine kinase inhibitors, making accurate identification of this tumour essential. Here, we report the case of a 38-year-old female patient with a tumour clinically resembling uterine leiomyoma. Microscopically, the spindled tumour cells were arranged in orderly intersecting fascicles, accompanied by a sparse infiltrate of inflammatory cells and a notable absence of myxoid matrix. Immunohistochemistry and molecular testing revealed an ALK::SYN3 fusion, suggesting the diagnosis of a uterine leiomyoma-like inflammatory myofibroblastic tumour (UL-like IMT). UL-like IMT is exceedingly rare and can easily be misdiagnosed as smooth-muscle tumours based solely on clinical manifestations and morphology. Therefore, it is recommended that the diagnosis be based on a combination of histopathological features, immunohistochemical markers, and genetic testing results to ensure a comprehensive and accurate assessment.