Gene dosage at 9p21 was successfully measured in 75 vertical growth phase primary melanomas (48 relapsers and 27 non-relapsers) using MLPA. Gene dosage ratios for 12 CDKN2A/CDKN2B locus sites and 11 other 9p gene sites were determined. Reduced gene dosage was more frequent in relapsers (Fig. 2). It can be seen that although loss of gene dosage occurred across 9p (especially in relapsers) the most common region of loss was between CDKN2A exon 1α (coding for CDKN2A) and MTAP. The median gene dosage at eight key regions across 9p, and their association with relapse or histological indicators of poor prognosis are presented in Table 1. Relapse was associated with loss at 9p21.3 overall (P = 0.04) and loss in regions coding for CDKN2A (one sided P = 0.03, two sided P = 0.05), and (borderline) associated with loss anywhere in the CDKN2A region (from CDKN2A CpG island probe to CDKN2A exon 3 probe) (one-sided P = 0.05, two-sided P = 0.1) but not elsewhere across 9p.