Challenges in the Diagnosis of Medulloblastoma Recurrence at an Unusual Site in a Patient With Prader-Willi Syndrome.

Medulloblastoma is the most common malignant pediatric brain tumor. Survival rates range between 50% and 80% depending on histology and other biologic features, metastases, and treatment approach. Prader-Willi syndrome (PWS) is a genetically inherited disorder characterized by dysmorphic features, mental retardation, obesity, and hypogonadism among other features. We describe a 10.5-year-old girl with PWS and previous standard-risk medulloblastoma that relapsed in the pons 3 years after the end of treatment. Diagnosis of relapse was delayed by a preceding varicella infection, an initial clinical/radiologic response to steroids and the unusual location, and was confirmed with a stereotactic biopsy. Second-line therapy was commenced, however, the patient rapidly deteriorated and died. This is the first report of medulloblastoma in a patient with PWS.

Flow cytometry of bone marrow aspirates from neuroblastoma patients is a highly sensitive technique for quantification of low-level neuroblastoma.

Background: Bone marrow involvement is an important aspect of determining staging of disease and treatment for childhood neuroblastoma. Current standard of care relies on microscopic examination of bone marrow trephine biopsies and aspirates respectively, to define involvement. Flow cytometric analysis of disaggregated tumour cells, when using a panel of neuroblastoma specific markers, allows for potentially less subjective determination of the presence of tumour cells. Methods: A retrospective review of sequential bone marrow trephine biopsies and aspirates, performed at Great Ormond Street Hospital, London, between the years 2015 and 2018, was performed to assess whether the addition of flow cytometric analysis to these standard of care methods provided concordant or additional information. Results: There was good concurrence between all three methods for negative results 216/302 (72%). Positive results had a concordance of 52/86 (61%), comparing samples positive by flow cytometry and positive by either or both cytology and histology.  Of the remaining samples, 20/86 (23%) were positive by either or both cytology and histology, but negative by flow cytometry. Whereas 14/86 (16%) of samples were positive only by flow cytometry. Conclusions: Our review highlights the ongoing importance of expert cytological and histological assessment of bone marrow results. Flow cytometry is an objective, quantitative method to assess the level of bone marrow disease in aspirates.  In this study, flow cytometry identified low-level residual disease that was not detected by cytology or histology. The clinical significance of this low-level disease warrants further investigation.