The methylation frequency in recurrence and progression tumours was consistently higher across all six genes compared to their no-recurrence counterparts; these differences were most pronounced for HOXA9 and ISL1 and achieved statistical significance for ISL1. Paradoxically, in HOXA9, no-recurrence, recurrence and progression tumours were less frequently methylated than in their low/intermediate-grade tumour counterparts. This evidence concerns the gene ISL1 and neoplasm.