Cancer

Introduction

The cancer incidence domain of the Atlas of Healthcare Variation gives clinicians, patients and providers an overview of the crude and age-standardised incidence rates both overall and for the five most common cancers in New Zealand, by district health board (DHB). The intention of this domain is to set the scene for future atlases to undertake a more detailed exploration of the diagnosis and management of certain cancer types.

Cancer is a leading cause of morbidity and mortality in New Zealand, accounting for nearly one third of all deaths.[1] Despite a decline in cancer mortality and an increase in cancer survival over time, it remains an important cause of preventable mortality and illness alongside cardiovascular disease. Smoking, nutrition, obesity, alcohol and lack of exercise are significant risk factors. For Māori and people living in socioeconomically deprived areas, the burden of cancer is much higher than for the general population.

While the overall risk of developing cancer in New Zealand is expected to stabilise or decline over the next decade, New Zealand has an increasing number of people who are developing cancer, mainly because of population growth and ageing.

Data sources and method

Data for this Atlas domain were drawn from the Ministry of Health’s New Zealand Cancer Registry (NZCR), which collects registration information about each tumour, as well as key demographic information. The registry includes all malignant cancer apart from superficial cancers of the skin (basal cell and squamous cell cancers of the skin). Melanoma is included. Read the cancer incidence atlas methodology.

Technically what are being presented are ‘registration’ rates – the rate cancers are being recorded in the cancer registry. Registration is a statutory obligation pursuant to the Cancer Registry Act 1993.

Incidence rates are presented for all cancers and then the five most common cancers separately. In the period 2008–2012 these were: female breast cancer, colorectal cancer, lung cancer, melanoma and prostate cancer (males only). These five cancers accounted for 63 percent of registrations. Data are presented for five years combined and the analyses by year are presented as three year rolling averages to allow for statistical robustness.

Standardisation

The incidence rates presented here are both crude and age-standardised rates (ASR). Age-standardisation adjusts rates to account for the age structure of the DHB population. This is important because cancer rates increase significantly with age. This means DHBs that have a population that is older than average will have higher rates of cancer than those with a younger population. Age-standardised data allows us to tell whether variation between DHBs is the result of age structure or not. In contrast, the crude rates show actual cancer incidence rates by DHB. These rates give information to enable regional population-level planning for cancer prevention and control.

Key findings

All cancers

• Over the five years, the crude rates did not vary significantly with an average of 487.3 crude cancer registrations per 100,000 population. The ASR however reduced slightly over the period to 352/100,000 population.
• The crude incidence of all cancers increased significantly with each age band, from 19/100,000 in those aged 0-24 years to 2,508/100,000 in those aged 75 years and over.
• This increase in cancer incidence with age means that the crude rates were significantly higher for non-Māori at 519/100,000 compared with 300/100,000 for Māori, due to the older age structure of the non-Māori population. Once standardised for age Māori have a cancer registration rate 27% higher than non-Māori.
• For both crude and ASR female registration rates were significantly lower than the male rates.
• There was a 1.6 fold variation between DHBs in crude cancer registration rates, with some DHBs having consistently higher rates over the five years. In contrast, there was no variation between DHBs in ASR for all cancers, with 1.1 fold variation. This reflects the differences in the demographics of the populations served by the DHB.

The table below shows the total number of cancer registrations over five years (2008–2012) by cancer type and by sex.

Table one: The number of commonly registered cancers, by sex, 2008–2012
Cancer	Males (count)	Cancer	Females (count)
Prostate	15,581	Breast	14,188
Colorectum and anus	7,629	Colorectum and anus	7,075
Melanoma	6,052	Melanoma	5,295
Lung	5,274	Lung	4,661

 

Female breast cancer

• Rates of female breast cancer did not vary over the five years, with crude rates of 129 cases per 100,000 women and ASR of 96/100,000.
• ASR were significantly higher for Māori at 124/100,000 compared with 91.8/100,000 in non-Māori women.
• Registrations increased significantly with each increasing age band.
• There was limited variation between DHBs in incidence rates.

Colorectal cancer

• Crude registration rates did not vary over the five years, remaining around 68 cases per 100,000 population, with ASR of 46/100,000.
• Colorectal cancer is one of the few cancers for which registration rates are lower in those identifying as Māori, although recently rates for Māori and non-Māori have begun to converge. Crude rates per 100,000 for Māori were 36.7 compared with 46.4 for non-Māori.
• As with other cancers, crude rates increased significantly with each increasing age band, with a sharp increase in rates from 45-64 and 65 and over.
• Males had significantly higher rates than females.
• Four DHBs appeared to have consistently higher registration rates with approximately 2.5 fold between DHBs, however variation was lower in the ASR at around 1.5 fold.

Lung cancer

• In the period 2008 to 2012, the crude rate of lung cancer registrations was 46.1 people/100,000. ASR were slightly lower at 32/100,000.
• Lung cancer rates increased with age from 2.7/100,000 people under 45 years to in excess of 290/100,000 for those aged 75 years and over.
• Māori had three times higher crude and ASR than non-Māori (82.3 compared to 26.8/100,000).
• Men had a higher lung cancer rate than women - 49.6/100,000 compared with 42.0/100,000.
• There was approximately a two-fold DHB variation in the crude lung cancer rates and 1.7 fold variation in ASR.

Melanoma

• Melanoma rates did not vary significantly over the years studied, with crude rates of 52/100,000 and ASR of 39/100,000.
• Those identifying as Māori had significantly lower crude and ASR of melanoma than non-Māori – with crude rates for Māori of 4.5/100,000 and for non-Māori of 61/100,000.
• Rates increased with age, and males had significantly higher rates than females.
• There was a two-fold variation in crude and ASR between DHBs. This suggests that factors other than age influence melanoma rates.

Prostate cancer

• Crude prostate cancer rates for males were on average 142/100,000 and ASR were slightly lower on 106/100,000.
• Prostate cancer rates were generally lower in Māori than non-Māori. Crude rates in Māori men were 52 per 100,000 compared with 162/100,000. The ethnic difference was reduced by age-standardisation to 85.4/100,000 Māori and 112.7/100,000 for non-Māori.
• Crude rates varied two fold by DHB and reduced to 1.6 fold variation for ASR.

Summary

These data show that over the period studied the crude incidence rates of all cancers and the five most common cancers varied up to two and half times by DHB. Age standardisation shows that age can explain many of these differences, but not all.

The demography Atlas presents by DHB life expectancy rates, ethnic composition, age bands and deprivation which might be useful in interpreting these cancer incidence data.

Presenting these data provide the context for future cancer-specific analyses exploring whether there is variation in the diagnosis and treatment.

Recommended reading

National Institute of Health and Care Excellence. 2015. Suspected cancer: recognition and referral. http://www.nice.org.uk/guidance/ng12/evidence/full-guidance-65700685.