Composite Neuroblastoma Metastatic to a Lymph Node: The Novel Histopathologic Diagnosis of a Unique Multiclonal Neoplasm.

Objective Composite neuroblastoma is a tumor composed of multiple tumoral clones within the neuroblastoma family. To date, establishing this unique histopathologic diagnosis has required the evaluation of the primary tumor mass. We report a case of composite neuroblastoma diagnosed by evaluation of a metastatic lymph node. Methods One abdominal lymph node involved by tumor was evaluated in a 6-year-old boy. The primary abdominal mass was not examined. Following histopathologic examination, clonality studies using comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH) were also performed. Results Two distinct tumor components were identified by histopathologic evaluation and classified as differentiating neuroblastoma (component A) and poorly differentiated neuroblastoma (component B). Based on the patient's age, each clone was further classified as Unfavorable Histology. The presence of these two different tumoral clones was confirmed by CGH and FISH. Conclusion This case affirms the histopathologic approach to evaluating composite tumors, as established by the International Neuroblastoma Pathology Classification (INPC) model for ganglioneuroblastoma, nodular tumors. Also, when both components are metastatic, this case demonstrates that composite tumors can be diagnosed by the evaluation of metastatic lesions alone. Finally, it supports the addition of composite neuroblastoma to a future version of the INPC.