How is a general practitioner (or a paediatrician, for that matter) to know that a child has a relatively rare disease such as cancer? The answer, perhaps, lies in a paediatric commonplace, an axiom of paediatric practice: listen carefully to the parents—they know their own child and are probably right. (Don't all medical students have that branded on their brain stems on their first day in paediatrics?) Axioms, of course, don't have to be proved; they are agreed starting points from which everything else follows. Paediatrics has but one axiom of axioms: the best interests of the child come before everything else. That's the ace of trumps in …