Spontaneous regression of metastatic cancer: learning from neuroblastoma.

Several interesting biological questions arise when thinking about the heterogeneous presentation of neuroblastoma, especially with regard to the molecular differences between very low- and high-risk disease. Why do some metastatic tumours spontaneously differentiate or regress entirely? Does the presence of disseminated disease always indicate metastases, or might some cases be better considered as multifocal disease?