Background
Evidence is emerging that melanoma has distinct etiologic pathways and subtypes, characterized by factors like anatomic site of the tumour. To explore genetic influences on anatomic subtypes and whether subtypes aggregate within families, we examined the extent to which melanomas in first-degree relatives of cases shared the same body site of occurrence.
Methods
Population-level linked data were used to identify the study population of over 1.5 million individuals born in Western Australia between 1945 and 2014. First-degree relatives were linked using the genealogical Family Connections System and family pairs diagnosed with melanoma were identified from Western Australian Cancer Registry data. There were 1,009 pairs of invasive tumours from 677 family pairs and anatomic site was categorized as head/neck, trunk, upper extremities, or lower extremities. Chi-Square tests evaluated site concordance between family pairs. Greater than expected representation of site-concordant pairs would suggest the presence of genetic factors that predispose individuals to site-specific melanoma.
Results
Comparing observed versus expected totals, we observed a modest increase in site concordance for invasive head/neck and truncal tumours (P=0.02). A corresponding analysis including in situ tumours showed a similar concordance (P=0.05). No further evidence of concordance was observed when stratified by sex.
Conclusions
Modest evidence of familial aggregation by anatomic site was observed but with inconsistent patterns between sites. Results suggest that further investigation into the familial aggregation of melanoma by tumour site is warranted, with the inclusion of genetic data in order to disentangle the relative contributions of genetic and environmental factors.