The aetiology of myeloma remains unknown Many risk factors
The aetiology of myeloma remains unknown. Many risk factors playing an important role in other cancers have not been clearly associated with myeloma , and most of the strongest myeloma risk factors still show inconsistent results. Some evidence points to obesity as an important risk factor for myeloma [11,12] whereas other studies have shown non-significant increases in risk [13,14]. Exposure to ionizing radiation, organic solvents and employment in agriculture have also shown conflicting results, and an inherited component has been suggested . How much of the incidence trends are attributable to improving case ascertainment in an ageing Oxidopamine hydrochloride rather than increasing obesity, and occupational and environmental exposures is uncertain.
Methods Mortality data were obtained from a data download of the mortality collection of the Ministry of Health . This information was available for 1988 to 2015 and included both ICD-9 and ICD-10 codes so no retrospective conversions were required. Population data by relevant ethnic group, sex, age and year were the mean annual population estimates from Statistics New Zealand . Age-specific incidence and mortality rates were calculated for each sex, from age 25 years for incidence and from age 40 years for mortality. Statistical tests for trends in age-specific rates were assessed using the method of Armitage . Age-standardised rates were calculated using the WHO standard population (WHO 2000–2025) and trends in age-adjusted rates, and heterogeneity of the trends, analysed using the Mantel-Haenszel extension chi-square test . To avoid any undue influence of the first time period, changes in age-standardised rates were expressed as an annual percentage change compared to the average rate over each relevant time period. Age-adjusted incidence and mortality rate ratios, and ratios of age-adjusted rates were calculated where appropriate.
Results Between 1985 and 2016 there were 7826 people registered by the NZCR as having a first diagnosis of multiple myeloma or plasmacytoma. Just over half were male and diagnoses were most commonly made between the ages of 70 and 79 years. Over 90% of diagnoses were in non-Maori: there were 635 diagnoses in Maori over the 32 years. The median age at diagnosis was 64 years for Maori and 72 years for non-Maori (Table 1). The incidence rate of myeloma increased with age: the incidence in 65–99 year olds was about 4-fold greater than in 45–64 year olds and about 30-fold greater than in 35–44 year olds. From 1988–2015, 4000 people died of myeloma, with a slightly higher proportion in men than women (Table 1). The median age at death was 67 years for Maori and 75 years for non-Maori. The overall age-standardised incidence rate (ASIR) for myeloma in 2015–2016 was 5.29 per 100,000 person-years (Table 2). In 2015–2016, Maori men had the highest ASIR of 8.81 followed by Maori women at 6.81 per 100,000 person-years. Over the same years, non-Maori men and women had ASIRs of 6.57 and 3.64, respectively, giving age-standardised incidence rate ratios for Maori to non-Maori of 1.37 (95% CI 1.00–1.85) for men and 1.94 (95% CI 1.40–2.68) for women. The incidence trends from 1985 showed significant heterogeneity across age groups so cannot meaningfully be combined. Between 1985 and 2016 the age-specific incidence rates of myeloma in the total population increased significantly for men in several age groups (Fig. 1 and Table 3). In women there was a suggestion of small increases but these did not reach significance. There was statistically significant departure from linearity in the oldest age groups so a linear trend could not be determined. The age-standardised incidence rates in non-Maori have increased significantly since 1991 in men (31% increase; p < 0.001) but not women (6.1% increase; p = 0.422) (Fig. 2). In all periods men have had significantly greater incidence rates compared to women, with male to female rate ratios ranging from 1.49 to 1.80, all statistically significantly greater than 1.0. In Maori the age-standardised incidence rates fluctuated more from year to year because of few diagnoses of myeloma (Fig. 2). Maori men had a non-significant linear increase in incidence of 21% and Maori women a non-significant linear increase of 17% over this time. The period-specific adjusted Maori male to female rate ratios also fluctuated widely.