PD-L1 expression and CD8+tumor-infiltrating lymphocytes are associated with ALK rearrangement and clinicopathological features in inflammatory myofibroblastic tumors

Background: Inflammatory myofibroblastic tumors (IMTs) are rare mesenchymal neoplasms that are composed of myofibroblastic cells accompanied by inflammatory infiltrate. We investigated the immune profiles of IMTs, including PD-L1 expression and proportion of CD8+ tumor-infiltrating lymphocytes (TILs), as well as its clinicopathological characteristics according to ALK gene rearrangement status. Methods: Twenty-eight IMTs from 25 patients were retrieved from our pathology files (2005-2015), and their clinicopathological parameters and outcomes were analyzed. Immunohistochemistry (IHC) was performed using whole-tissue sections to detect PD-L1 and CD8 expression, and fluorescent in situ hybridization (FISH) analysis and IHC were performed using tissue microarrays to identify rearrangements in the ALK, ROS1, and RET genes. Results: ALK rearrangement was observed in 11 cases (44.0%), and all cases exhibited diffuse cytoplasmic ALK expression during IHC. ROS1 or RET rearrangement was not detected using IHC or FISH. IMTs harboring ALK rearrangement (ALK-positive) were located in the lungs (n = 7), genitourinary tract (n = 2), and mesentery (n = 1). The mean patient age was 33.2 years for ALK-positive IMTs and 53.1 years for ALK-negative IMTs. All patients with ALK-positive IMTs survived without recurrence or metastasis. IMTs with metastasis and/or recurrence were ALK-negative and exhibited elevated PD-L1 expression (positive tumor cells: 70.0% vs. 21.3%, P = 0.023; H-score: 107.5 vs. 26.3, P = 0.005). In addition, ALK-negative IMTs had a more CD8+ TILs, compared to ALK-positive IMTs (23.3% vs. 8.9%, P = 0.027). Conclusion: ALK-positive IMTs are characterized by younger age, well-defined margins, frequent involvement of the lung, and fewer CD8+ TILs. Greater PD-L1 expression was observed in IMTs with tumor necrosis and metastasis/recurrence, which were also negative for ALK rearrangement. These results suggest that immune checkpoint inhibitors may be a novel option for treating patients with advanced IMT.