Clinical and histologic factors associated with melanoma thickness in New Zealand Europeans, Maori, and Pacific peoples.

BACKGROUND

Thickness is the major prognostic indicator for patients with melanoma. In many countries, the incidence of thick melanoma has not decreased. To reduce mortality, knowledge of the characteristics associated with melanoma depth is needed.

METHODS

To examine the relation between melanoma thickness and other factors in Europeans, Maori, and Pacific peoples, the authors analyzed the 14,802 melanoma registrations in New Zealand between 1996 and 2006. Notifications of invasive cutaneous melanoma from 1996 to 2006 were extracted from the New Zealand Cancer Registry. Ethnicity was categorized using the Statistics New Zealand prioritization algorithm. The geometric mean tumor thickness was calculated using log-transformed Breslow depth. Multivariate linear regression was used to examine the relation of predictor variables, their interactions, and melanoma thickness.

RESULTS

Melanoma thickness increased by 1% per year from 1996 to 2006. Although melanoma is rare in Maori and Pacific peoples, after adjustment, melanoma thickness was significantly greater in those populations compared with Europeans. Among Europeans, melanoma thickness was associated significantly with age at diagnosis, year of registration, sex, histology subtype, and extent of disease at diagnosis. In Maori, thick melanomas were likely to be nodular and to have regional or lymph node spread. The most important determinant of melanoma thickness in Pacific peoples was body site.

CONCLUSIONS

Differences in melanoma thickness among ethnic groups were not explained fully by tumor subtype, site, or extent of disease. The current results indicated that the thicker melanomas in darker skinned populations probably can be accounted for in part by more aggressive lesions. Research is needed to identify additional characteristics to explain ethnic variations in melanoma thickness.