The Rb tumours comprised two cohorts: Cohort 1, made up of nine tumours, where two distinct RB1 mutations were previously identified in each tumour; Cohort 2 comprised ten tumours, where seven had only one RB1 mutation, and in three, RB1 mutations remained either elusive (one tumour) or could not be satisfactorily confirmed by clinical screening methods (two tumours). The gene discussed is RB1; the disease is neoplasm.