Epidermal Growth Factor Gene Polymorphism and Development of Cutaneous Melanoma

Abstract

Identification of genetic factors predisposing to cutaneous melanoma (CM) has been the subject of considerable effort by many laboratories worldwide. Despite this, relatively few genetic factors mediating susceptibility to and/or prognosis in sporadic CM have been identified with certainty, although the literature contains a number of claimed associations. For example, polymorphisms associated with the melanocortin-1 receptor (MCR1) (Valverde et al, 1996; Kennedy et al, 2001), CDKN2A (Kumar et al, 2001), XRCC3 DNA repair (Winsey et al, 2000) genes, and glutathione S-transferase Mu phenotype (GSTM1) (Lafuente et al, 1995) may be associated with susceptibility to CM. Polymorphisms associated with the Vitamin D receptor and the cytochrome P450 CYP2D6 genes have been implicated in modulating prognosis in this tumor (Strange et al, 1999; Hutchinson et al, 2000). Several lines of evidence also suggest that CM patients develop an immune response to their tumors (Wolfel et al, 1993), supported by variable HLA-DQB1 allelic associations with CM susceptibility and prognosis (Lee et al, 1994; Bateman et al, 1998). In addition, interleukin-10 (IL10) promoter genotypes may confer both susceptibility to CM and act as risk factors for more advanced, invasive, poorer prognosis disease (Howell et al, 2001) and poorer survival (Martinez-Escribano et al, 2002), while gene polymorphisms associated with pro-angiogenic cytokines (in particular, vascular endothelial growth factor (VEGF)) may also play a role in predisposition to and tumor growth in CM (Howell et al, 2002). In the majority of these preliminary studies, probability values and odds ratios (ORs) for association tend to be modest, sample sizes small, and few—if any—independent verifications have been performed, so most results should be interpreted with caution. One such report (Shahbazi et al, 2002), demonstrating a highly significant association between a functional single nucleotide polymorphism (SNP) in the epidermal growth factor (EGF) gene (chrom 4q25–q27) and both susceptibility to/severity of this disease, generated considerable interest. In this study of 135 CM patients and 99 controls, the EGFþ 61 GG genotype, associated with elevated EGF expression, was associated with both CM susceptibility (47.4% in cases vs 20.2% in controls; po0.001; OR1⁄4 4.9) and tumor Breslow thickness as a surrogate marker of prognosis (p1⁄4 0.045 for tumors with a thickness of X3.5 mm vs o3.5 mm). This result is in agreement with a putative role for EGF in melanomanesis, due to its mitogenic and tumorigenic properties and action in proliferation of epidermal tissues, but again was based on analysis of a relatively small number of cases and controls. Accordingly, a number of independent studies, including a previous publication from our own laboratory (McCarron et al, 2003), one very recent paper (Amend et al, 2004), and two studies published in this issue (James et al, 2004; Randerson-Moor et al, 2004) have sought independent confirmation of the reported association between CM susceptibility and tumor Breslow thickness as a marker of disease severity and prognosis. The small study (159 patients and 310 controls) published by our group failed to demonstrate any association between EGF þ61 genotype and CM susceptibility. However, this study did show a modest, but significant increase in frequency of the GG genotype among patients with tumors 43.5 mm thick (30% vs 9.8%; p1⁄40.03), although the GG genotype was much less frequent among patients with thicker tumors than in the original study by Shahbazi et al (75.0%) (McCarron et al, 2003). The results from the McCarron et al study should be treated with some caution, since all patient genotyping was performed on DNA derived from archival tissue blocks and results could therefore be affected by any loss of heterozygosity for the EGF region within the tumor, although the methodology employed should be capable of detecting allelic sequences from surrounding and infiltrating non-tumor cells. Results from the two studies published in this issue (James et al, 2004; Randerson-Moor et al, 2004) and the recent communication in Cancer Research (Amend et al, 2004) are therefore of particular value, since all analyses were performed on DNA extracted from peripheral blood. Again, none of the three studies demonstrated any association between EGF þ 61 genotype and susceptibility to CM. This is noteworthy, because the two studies published in this issue examined considerably larger numbers of patients and controls (753 and 380 patients, compared with 2387 and 697 controls respectively) than either of the earlier studies. In addition, both of these studies report no EGF þ61 genotypic association with nevus phenotype or development not examined hitherto, while the study by Amend et al (2004) did not show any association with multiple versus single primary melanoma status. The three studies by Amend et al (2004), James et al (2004) and Randerson-Moor et al (2004), however, report conflicting findings with respect to EGF þ61 genotype and tumor Breslow thickness. James et al (2004) report that CM patients homozygous for the GG genotype do have thicker Abbreviation: CM, cutaneous melanoma