MITF E318K settles as a moderate-penetrance melanoma allele

Design

systematic review with meta-analysis of 11 retrospective case-control studies

Population

8,606 melanoma patients and 17,953 controls, predominantly European-ancestry cohorts

Primary outcome

melanoma risk associated with germline MITF variants

Effect

E318K in 2.1% of patients vs 0.8% of controls; odds ratio 2.55 (95% CI 1.90–3.43); enrichment for >200 naevi with odds ratios up to 12.4 in multiple-melanoma cohorts

The MITF E318K variant has been linked to melanoma for over a decade, with uncertainty about how large the risk is and whether it extends to other cancers. This systematic review pooled 11 retrospective case-control studies: 8,606 melanoma patients and 17,953 controls.

The variant was present in 2.1% of melanoma patients and 0.8% of controls, an odds ratio of 2.55 (95% CI 1.90–3.43). The association strengthened with multiple primary melanomas — carrier frequency up to 2.6% against 1.0% in single-melanoma cases, with odds ratios reaching 4.45 in individual studies. Phenotypically, carriers were enriched for high naevus burden, with odds ratios up to 12.4 in multiple-melanoma cohorts for more than 200 naevi. No consistent association appeared with age at onset or pigmentary traits.

The non-melanoma claims do not survive. One study reported raised renal cancer risk with an odds ratio of 7.64 and larger cohorts did not replicate it; an association with phaeochromocytoma and paraganglioma at 3.19 has no confirmation. No other MITF variant showed significant cancer risk. So this is a melanoma susceptibility allele of moderate penetrance, and the extended tumour spectrum that sometimes appears in counselling material is not supported.

• An odds ratio of 2.55 is moderate penetrance — surveillance intensity, not prophylactic decisions.
• Do not counsel MITF E318K carriers about renal cancer or phaeochromocytoma risk; neither association is replicated.
• The phenotype that should prompt genetic referral is multiple primary melanomas or a very high naevus count, not a single melanoma.
• Melanoma in Indian populations is predominantly acral and mucosal, where naevus-count and pigmentary risk models do not apply — this variant is studied almost entirely in European-ancestry cohorts.
• Whole-body skin examination and photographic surveillance remain the intervention, with or without the genotype.

Why it matters

It draws a line under a tumour spectrum that had been creeping into counselling on the strength of single unreplicated studies.

Don't overread it

Retrospective case-control studies in melanoma cohorts — this estimates relative risk in selected populations, not absolute lifetime risk for a carrier.

The statistics, in plain English

The carrier frequencies are small — 2.1% against 0.8% — so an odds ratio of 2.55 sits on a low absolute base, and the increase in lifetime melanoma risk for an individual carrier is much less dramatic than the ratio suggests. The odds ratios of 4.45 and 12.4 come from individual studies and specific subgroups rather than the pooled analysis, which is where selective quotation usually happens. These were retrospective case-control studies, a design that overstates risk when cases are ascertained through familial melanoma clinics.

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