Renal Inflammatory Myofibroblastic Tumor in an Infant: Case Report with Review of Literature

Inflammatory myofibroblastic tumor (IMT) is an intermediate-grade neoplasm of myofibroblastic lineage occurring due to a cytogenetic clonal abnormality of chromosome 2p23. Pediatric renal IMTs are rare and infant renal IMTs are almost anecdotal. We herein report a 1-year-old female child who presented with a firm mass in the right lumbar region. Biopsy, and later, surgical resection revealed a tumor composed of spindle cells with intermixed plasma cells. On immunohistochemistry (IHC), the lesional cells were positive for smooth muscle actin and anaplastic lymphoma kinase (ALK). A diagnosis of IMT was made based on morphology and IHC. Diagnosis of renal IMTs become challenging especially in a tiny biopsy wherein clear cell sarcoma of kidney, Wilms tumor with predominant mesenchymal component, congenital mesoblastic nephroma, and metanephric stromal tumor are the differential diagnoses in this age group. Renal IMTs generally have better prognosis as compared to extrarenal IMTs. Approximately, 50 to 60% of these tumors harbor ALK gene rearrangement as demonstrated by positivity for ALK IHC. ALK inhibitors like crizotinib or ceritinib can be given for advanced metastatic tumors.