Identification of the molecular characterization and tumor microenvironment of thoracic inflammatory myofibroblastic tumors.

Background: Inflammatory myofibroblastic tumors (IMTs), rare soft tissue neoplasms, are characterized by a blend of myofibroblastic proliferation and inflammatory features. While generally characterized by slow growth, IMTs can exhibit locally aggressive behavior, and in rare instances, metastasize to distant sites. This study elucidated the clinical characteristics, molecular profile, and tumor microenvironment of thoracic IMTs. Methods: We retrospectively analyzed cases of IMTs diagnosed at the National Taiwan University Hospital between 2000 and 2020. ALK immunohistochemistry (IHC) was performed, followed by fluorescence in situ hybridization (FISH) for confirmation. Next-generation sequencing (NGS) was employed to detect unknown oncogenic drivers, and multiplex immunofluorescence staining was used to characterize the tumor microenvironment. Demographic, clinicopathological characteristics, and treatment outcomes were systematically recorded and analyzed. Results: We identified a total of 8 patients with thoracic IMTs, whose median age of the participants was 33.8 years (range: 18.6–58.7). The disease status of all tumors were early-stage, and all patients underwent surgical excision. ALK fusions were detected in 6 tumors (all spindle-cell patterns), with fusion partners including 3 TPM3, 2 DCTN1, and one EML4. In the remaining 2 tumors without ALK fusion, NGS showed NTRK3 alteration with high gene expressions. Multiplex IHC of three cases identified a pronounced infiltration of macrophages cells within the tumor microenvironment. Conclusion: Patients with thoracic IMT patients are typically young with early-stage disease. ALK fusion were the most common genetic alteration, particularly in spindle-cell patterns. Characterization of the tumor microenvironment indicates the potential of immune profiling in the tumor biology and targeted immunotherapy approaches.