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. Author manuscript; available in PMC: 2018 Oct 1.
Published in final edited form as: JAMA Dermatol. 2017 Oct 1;153(10):1026–1031. doi: 10.1001/jamadermatol.2017.2444

Table 2.

Phenotypic Characteristics and MC1R Status in Relationship to Histopathologic Pigmentation in Incident Primary Melanomas from 2387 patients in the GEM Study

Amelanotic vs. Pigmented Melanoma
Pigmented Melanoma Amelanotic Melanoma Study Design Featuresb Study Design Features + Phenotypec Study Design Features + Phenotype + MC1Rd
Characteristics (n = 2209)a (n = 178)a OR (95% CI) P Valuee OR (95% CI) P Valuee OR (95% CI) P Valuee
Phenotype
Back nevi
 Present 1904 (86.2) 139 (78.1) 1 [Reference] 0.006 1 [Reference] 0.01 1 [Reference] 0.01
 Absent 305 (13.8) 39 (21.9) 1.76 (1.18–2.65) 1.71 (1.14–2.57) 1.68 (1.12–2.53)
Freckles
 None to few 1912 (86.6) 143 (80.3) 1 [Reference] 0.007 1 [Reference] 0.03 1 [Reference] 0.10
 Many 297 (13.4) 35 (19.7) 1.76 (1.17–2.65) 1.58 (1.04–2.39) 1.44 (0.93–2.22)
Phenotypic indexf
 Sun-resistant phenotypic index 989 (47.1) 68 (38.2) 1 [Reference] 0.006 1 [Reference] 0.02 1 [Reference] 0.03
 Sun-sensitive phenotypic index 1109 (52.9) 110 (61.8) 1.57 (1.14–2.18) 1.48 (1.07–2.07) 1.44 (1.03–2.01)
Genetics
MC1Rg
 wt/wt 357 (16.2) 23 (12.9) 1 [Reference] - - 1 [Reference]
 r/wt or R/wt 980 (44.4) 69 (38.8) 1.17 (0.71–1.93) - - 1.16 (0.70–1.92)
 r/r, R/r, or R/R 872 (39.5) 86 (48.3) 1.70 (1.04–2.78) - - 1.43 (0.86–2.39)
P value for trend 0.01 - - 0.13

Abbreviations: CI, confidence interval; GEM, genes, environment, and melanoma; MC1R, melanocortin 1 receptor; MPM, multiple primary melanoma; OR, odds ratio; SPM, single primary melanoma.

a

Data are given as number (percentage) of melanomas unless otherwise specified.

b

Adjusted for study design features: sex, age, study center, and lesion status (SPM or index MPM)

c

Adjusted for study design features, freckling, back moles, and phenotypic index.

d

Adjusted for study design features and all characteristics displayed in the table.

e

P values were calculated according to logistic regression models and P values for trend were calculated including MC1R categories as ordinal variables.

f

Phenotypic index was calculated by additively combining: hair color (black or dark brown=0; light brown or blonde=1; red=2), eye color (brown=0; grey, green, or hazel=1; blue=2), and ability to tan (deeply or moderately=0; occasionally or none=1). Those with index scores of 0,1, or 2 were categorized as having a sun-resistant phenotypic index. Patients with index scores of 3, 4, or 5 were categorized as having a sun-sensitive phenotypic index.

g

MC1R “R”: D84E, R142H, R151C, R160W, and D294H, all nonsense and insertion/deletion; “r”: all other variants; “wt”: consensus.