RB1 and hyperinsulinemic hypoglycemia, familial, 4: IHC has some potential advantages for determining RB status: (i) IHC requires minimal tumour material, which is a common obstacle in these clinical samples, (ii) RB deficiency is detected even when there is loss due to mechanisms other than bi-allelic deletion, such as nonsense mutations and (iii) direct visualization of individual cells allows precise interpretation in cases that contain a large proportion of stroma, which may confound next-generation sequencing (NGS) and CGH array analyses.