Aims: To investigate regional variation in myeloma incidence in New Zealand in order to inform aetiological investigations.
Methods: All new registrations of myeloma (1991-2016) were extracted from the New Zealand Cancer Registry. Ethnic classifications used prioritised ethnicity. For geographical groupings, 74 Territorial Local Authority (TLA) categories for 2006 and population densities were used. Negative binomial regression was used to estimate incidence rate ratios, 95% confidence intervals and p-values.
Results: Between 1 January 1991 and 31 December 2016, 7,083 myelomas were registered. The Clutha TLA had a significantly lower incidence than the New Zealand average. Compared to Clutha, many regions had a significantly higher incidence, but there was no clear spatial pattern. The highest incidence rate was for Māori men in the North Island. Women had significantly lower incidence than men of the same ethnic group and in the same area.
Conclusions: As both extremes of myeloma incidence occurred in rural areas, and as all TLAs (except one, Horowhenua) in the two lowest risk categories were rural, it seems unlikely that farming confers an increased risk. Results suggest that some other factor is driving the differences in myeloma incidence by ethnic group. We have provided a baseline of the geographical burden of myeloma in New Zealand.