Case Report: Single-cell transcriptomic profiling of a pediatric ALK-negative gastric inflammatory myofibroblastic tumor.

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm, approximately 50% of which harbor ALK rearrangements. ALK-negative gastric IMT (G-IMT) in pediatric patients is exceptionally rare and poorly characterized. We report a 6-year-old male with fever, melena, and severe anemia (Hb 30 g/L). Imaging revealed a gastric fundus mass, and subtotal gastrectomy confirmed IMT with dense plasma-cell infiltrate and negative ALK immunostaining. We performed single-cell RNA sequencing on tumor and paired adjacent non-tumor tissue (14,103 cells). CellChat analysis inferred prominent CXCL12-CXCR4 communication between neoplastic myofibroblasts and immune cells. Macrophage subclustering identified an S100A9-high inflammatory tumor-associated macrophage state, and pseudotime analysis placed this state along a continuous transcriptional ordering with resident-like macrophages. To our knowledge, this is the first single-cell transcriptomic characterization of pediatric ALK-negative G-IMT and provides hypothesis-generating insight into its inflammatory microenvironment.