Inflammatory myofibroblastic tumors: recent progress and future of targeted therapy

An inflammatory myofibroblastic tumor is a rare component of bone and soft-tissue sarcomas that has distinct pathological features as a lymphoplasmacytic inflammatory infiltrate. As is the case for other non-small round cell sarcomas, surgical resection remains the standard treatment strategy for inflammatory myofibroblastic tumors, but recurrence is possible. Concerning systemic therapy, the available data for conventional chemotherapy (such as those of doxorubicin-based regimens) are limited, and case reports of anti-inflammatory inflammatory myofibroblastic tumor treatments describe some degree of symptom relief and efficacy against tumor progression. However, as more information about cancer genomics accumulates, the potential for molecularly targeted therapies for inflammatory myofibroblastic tumors has become more promising. Approximately half of inflammatory myofibroblastic tumors harbor anaplastic lymphoma kinase (ALK) fusion genes, and the other half could have potentially targetable fusion genes or mutations such as ROS1, NTRK and RET; case reports demonstrating the clinical efficacy of treatments targeted to inflammatory myofibroblastic tumor have been published, as have several prospective clinical trials. Few drugs are approved for the treatment of inflammatory myofibroblastic tumor, and most of them were approved for tumor-agnostic indications. Drugs that could be used for pediatric indications and dosing in inflammatory myofibroblastic tumor have also not been established. To provide effective targeted therapy for rare diseases such as inflammatory myofibroblastic tumor, it is necessary to obtain clinical evidence by designing and performing clinical trials and to find a path toward regulatory approval. The pathological, clinical features of inflammatory myofibroblastic tumor and the current progress of targeted therapy such as ALK, ROS1 or NTRK inhibitors are summarized in the review.