Paediatric tumours are molecularly distinct from those encountered in adult practice. They carry an unusually low mutational burden, and are driven less often by point mutations than by gene fusions, structural rearrangements and epigenetic dysregulation. As a result, the molecular panels developed for adult oncology frequently fail to capture the drivers of childhood cancer, and a dedicated diagnostic toolkit is required.

This talk argues that paediatric cancer has not simply borrowed from adult oncology, but has been central to building the field of molecular pathology itself. From the two-hit model of tumour suppression, through the translocations that established FISH as a diagnostic technique, to the methylation classifiers now reshaping the diagnosis of brain and soft-tissue tumours, many of the foundational concepts in cancer genetics originate in childhood cancers.

The presentation reviews the current molecular toolkit (FISH, PCR, NGS, whole genome sequencing and DNA methylation arrays), outlining the strengths and limitations of each. Particular attention is given to methylation profiling, which has become the most informative single test for tumours with too few mutations, and too ambiguous a morphology, to classify by other means.

Clinical cases are used to illustrate the toolkit in practice, each selected to demonstrate a different principle: when to escalate testing, when a simpler test suffices, and how readily a diagnosis can be lost or recovered depending on which test is chosen. The underlying message is that molecular testing sharpens clinical judgement, rather than replacing it.

The talk shall serve as an overview of non gestational placental tumours. Included topics include chorangioma, inflammatory myofibroblastic tumours and both fetal and maternal metastatic disease to the placenta.