- Patients must have at least one measurable PN, defined as a lesion of at least 3 cm measured in one dimension; patients who underwent surgery for resection of a PN are eligible provided the PN was incompletely resected and is measurable as per criteria above; measurability and suitability for volumetric MRI analysis of the target PN must be confirmed with the National Cancer Institute (NCI) Pediatric Oncology Branch (POB) prior to enrolling a patient; the target PN will be defined as the clinically most relevant PN, which has to be amenable to volumetric MRI analysis; PN will be classified as "typical" or "nodular" prior to enrollment