Inflammatory myofibroblastic tumors (IMTs) are rare sarcomas composed of myofibroblastic and fibroblastic cells, accompanied by inflammatory cell infiltration. Many IMTs exhibit clonal rearrangement of anaplastic lymphoma kinase (ALK). We herein report a 56-year-old woman with uterine IMT harboring a thrombospondin-1::ALK fusion that developed after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Laboratory data before systemic therapy indicated increased interleukin-6 and severe leukocytosis. The patient was treated with lorlatinib; however, the response duration was approximately two months. Similar case reports need to be compiled and evaluated to elucidate the efficacy of lorlatinib in post-allo-HSCT IMT with ALK rearrangement.