Advanced molecular pathology for rare tumours: A national feasibility study and model for centralised medulloblastoma diagnostics

Aims: Application of advanced molecular pathology in rare tumours is hindered by low sample numbers, access to specialised expertise/technologies and tissue/assay QC and rapid reporting requirements. We assessed the feasibility of co-ordinated real-time centralised pathology review (CPR), encompassing molecular diagnostics and contemporary genomics (RNA-seq/DNA methylation-array). Methods: This nationwide trial in medulloblastoma (<80 UK diagnoses/year) introduced a national reference centre (NRC) and assessed its performance and reporting to World Health Organisation standards. Paired frozen/formalin-fixed, paraffin-embedded tumour material were co-submitted from 135 patients (16 referral centres). Results: Complete CPR diagnostics were successful for 88% (120/135). Inadequate sampling was the most common cause of failure; biomaterials were typically suitable for methylation-array (129/135, 94%), but frozen tissues commonly fell below RNA-seq QC requirements (53/135, 39%). Late reporting was most often due to delayed submission. CPR assigned or altered histological variant (vs local diagnosis) for 40/135 tumours (30%). Benchmarking/QC of specific biomarker assays impacted test results; fluorescent in-situ hybridisation most accurately identified high-risk MYC/MYCN amplification (20/135, 15%), while combined methods (CTNNB1/chr6 status, methylation-array subgrouping) best defined favourable-risk WNT tumours (14/135; 10%). Engagement of a specialist pathologist panel was essential for consensus assessment of histological variants and immunohistochemistry. Overall, CPR altered clinical risk-status for 29% of patients. Conclusion: National real-time CPR is feasible, delivering robust diagnostics to WHO criteria and assignment of clinical risk-status, significantly altering clinical management. Recommendations and experience from our study are applicable to advanced molecular diagnostics systems, both local and centralised, across rare tumour types, enabling their application in biomarker-driven routine diagnostics and clinical/research studies.