Thoracic inflammatory myofibroblastic tumors: A decade-long retrospective study integrating clinicopathological and...

Inflammatory myofibroblastic tumors (IMT) are mesenchymal neoplasms of intermediate malignant potential, characterized by recurrent gene fusions in potentially targetable receptor tyrosine kinases. Primary thoracic IMTs are rare, and their molecular landscape remains incompletely characterized. A ten-year retrospective (2014-2024) clinicopathological analysis of primary thoracic IMTs was done. Histomorphological evaluation and molecular characterization by a graded approach incorporating immunohistochemistry, fluorescence-in-situ hybridization, multiplex reverse-transcription polymerase chain reaction, and next-generation targeted panel sequencing were performed for the common implicated driver fusions. Thirty IMTs involving the lung (n=17), tracheobronchial tree (n=12), and pleura (n=1) were identified. Median age at diagnosis was 18 years (range: 2 to 51 years), including 14 paediatric and 16 adult patients. Male: female ratio was 2.2:1 and 1.3:1, in adults and children, respectively. Majority (22/30, 73.3%) showed cellular spindle-cell pattern with lymphoplasmacytic inflammation. None showed significant atypia, necrosis, or mitotic activity. Molecular characterisation achieved in 22/30 cases revealed 73.3% (16/22) ALK-IMTs, 23% (5/22) ROS1-IMTs, and a single NTRK3-IMT. No statistically significant differences were seen among molecular subgroups, although ALK-IMTs were diagnosed at a higher median age (24.5 years) as compared to ROS1-IMTs (15 years). On follow-up (median follow up period: 24 months), local recurrence was observed in 23% (3/13) patients, all harbouring ALK-IMTs, one of whom was successfully treated with ALK inhibitor therapy; no disease-related deaths were recorded. Primary thoracic IMT affects children and young adults. Majority are driven by ALK gene rearrangements, followed by ROS1 alterations, underscoring role of molecular profiling in potential therapeutic stratification.