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| Journal of the New Zealand Medical Association,
30-November-2007, Vol 120 No 1266
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Women with breast cancer in Aotearoa New Zealand: the
effect of urban versus rural residence on stage at diagnosis and
survival
Hayley Bennett, Roger Marshall, Ian Campbell, Ross
Lawrenson
Urban/rural health inequalities have been identified and
prioritised in several countries during the past decade. Australia, the United
States, and Canada have all found that people living in regional and remote
areas have higher mortality rates than people living in urban and suburban
areas.1–5 The major contributors to
excess mortality in regional and remote areas appear to be circulatory disease,
injury (intentional and unintentional), respiratory disease, and
cancer.1,2
With respect to cancer, both later stage at diagnosis and
poorer survival have been shown in rural residents. Campbell et al investigated
over 60,000 patients in Scotland diagnosed with one of six common cancers, and
increasing distance from cancer centre was found to be associated with poorer
survival. Moreover, a follow-up study by the same research group found that
those living further from cancer centres were more likely to present with
advanced cancer at diagnosis, and this was thought to account for most of the
rural survival disadvantage.6,7
Similar results have been found for rural residents with
cancer in the United States, France, and
Australia.8–10 Regarding breast cancer
specifically, a systematic literature review revealed at least three studies
showing rural residents to be more likely to be diagnosed at a later stage of
breast cancer than their urban
counterparts.11–13 There was only one
study that suggested a survival disadvantage for rural women with breast
cancer.14
In New Zealand (NZ), while there are concerns about access
for rural patients, little national research compares health outcomes of urban
and rural residents. Two of the only such studies done in NZ (on breast and
upper gastrointestinal cancer) did not show any difference in cancer outcome by
urban/rural residence.15,16
This study set out to further explore the question of
possible urban/rural health disparity, looking at a recent cohort of women with
breast cancer, and using a number of different classification systems for urban
and rural residence.
MethodsWomen with a diagnosis of breast cancer (ICD-10 code
C50) in the New Zealand Cancer Registry (NZCR) between 1 January 1998 and 31
December 2002 were identified (n=11,340); 13 women appeared in the dataset twice
because they were registered for a second breast cancer.
Data on date of diagnosis, stage at diagnosis, age,
ethnicity, domicile code, and date of death (where death occurred) was supplied
by the New Zealand Health Information Service (NZHIS). Domicile code was then
matched to an urban/rural residence group and a deprivation score using the NZ
Deprivation Score (NZDep) 1996.17
Urban and Rural were classified in three different
ways. Firstly the standard Statistics New Zealand classification, based on
population size, was used to divide the cohort into main urban areas
(≥30,000 population), secondary urban areas (10–29,999 population),
minor urban areas (1000–9999 population), and rural areas (<1000
population).18
The second classification used was the Urban-Rural
Profile Classification, which is based on a comparison between a person's
residential address and their workplace address. Main urban areas remain the
same, but two other urban categories are defined by the percentage of residents
who are employed in a main urban area (see Figure 1).
Satellite urban communities have 20% or more of their
working population employed in main urban areas, whilst independent urban
communities have less than 20% of their workers employed in main urban areas.
The previously defined rural areas are split into four categories, again on the
proportion of residents employed in urban areas. This classification thus
defines urban and rural areas on the strength of social and economic ties to
urban centres, and aims to capture more of the heterogeneity that exists in
rural areas.
A rural area with high urban influence (with many
residents working in a nearby urban area) is likely to have ready access to
urban amenities and services, whereas a rural area with low urban influence will
be much more isolated from such
services.18
Figure 1. Urban-Rural Profile
Classification18
 The third method for classifying urban or rural
residence was to use distance from major cancer centre. Circles were drawn on a
large map in bands of distance around the six major cancer centres (Auckland,
Hamilton, Palmerston North, Wellington, Christchurch, and Dunedin). Each case's
domicile code was located in one of the distance bands of 0–10,
11–25, 26–50, 51–100, 101–200 and >200
kilometres.
Ethnicity, age, and socioeconomic status have all been
shown to affect cancer stage at diagnosis and/or
survival,19–22 and were thus deemed to be
important confounding variables requiring adjustment in multivariate regression
analysis.
Adjustment for cancer stage was also done in the
survival analysis. NZCR prioritised ethnicity codes were collapsed into three
groups: Māori, Pacific, and non-Māori/non-Pacific—any indication
of Māori ethnicity means the individual is prioritized to the Māori
ethnic group; age was also entered as a categorical variable in 15-year age
brackets. One of the age brackets (50–64 years) was the eligible age-range
for BreastScreen Aotearoa during the time of this study. Deprivation score was
included in the models as a continuous variable
Logistic regression was used to investigate the effect
of urban/rural residence on stage at diagnosis. Stage was dichotomised into
“early stage” (localised disease with no nodal involvement = 0) and
“late stage” (regional/remote disease = 1). Hosmer-Lemeshow goodness
of fit tests confirmed that the logistic model was an adequate fit for the data
for all analyses.23 Cox proportional hazards
regression was used for survival analysis.24
Survival time was the time from breast cancer diagnosis to death (in days) for
cases who died. For women still alive, survival time was deemed to be censored
at February 2006 (in accordance with the most up to date mortality data in the
NZHIS data extract). Stata® version9 was the statistical package
used.25
ResultsIn the 5 years spanning 1998–2002 there were 11,340
cases of female breast cancer registered in the NZCR. Table 1 shows that
approximately three-quarters of women were ≥50 years of age. Most of the
cohort were of non-Māori/non-Pacific ethnicity (89.2%); 8.2% were
identified as Māori and 2.7% as Pacific.
Stage at diagnosis was fairly evenly split with 45.5% at
“early stage” (localised disease) and 37.1% at “late
stage” (regional and remote disease). For 17.4% of cases the stage was
recorded as not stated/not known, and this was similar for both rural and urban
women. In the 4406 women aged 50–64 years, who would have been eligible
for BreastScreen Aotearoa, 53.9% were categorised as "early stage", 34.6% as
"late stage", and only 11.5% as stage not stated/not known.
Main urban areas were home to 71.6% of the study cohort
according to the population size-based classification, while 18% lived in
secondary and minor urban areas, and just over 10% lived in rural areas. In
comparison, using the Urban-Rural Profile Classification, 73.3% lived in main
urban areas, 3.3% in satellite urban communities, 13.3% in independent urban
communities, and 10.2% collectively in rural and remote areas.
Just under a third of the cohort lived within 10 km of a
cancer centre. Another third lived between 11–50km, 15% lived between
51–100km, and the remaining 22.3% lived over 100 km away from a cancer
centre.
In the analysis of the effect of urban/rural residence on
breast cancer stage at diagnosis, the 1977 cases with stage not stated/not known
were excluded (thus leaving 9363 cases).
The number of cases in the highly rural/remote, and distance
>200 km categories was very small, and thus these categories were analysed
together with the rural area with low urban influence and 101–200 km
distant groups respectively.
Table 1: Characteristics of the study
cohort
*3 cases unable to be assigned an Urban-Rural
Population Category (because no domicile code recorded in registry); †37
cases unable to be assigned an Urban-Rural Profile Category and ‡39 cases
unable to be assigned a distance (3 with no domicile code and other women living
in island, oceanic, or inlet areas).
Table 2 shows the results of three separate logistic
regressions. Urban/rural residence, however classified, did not have any
significant effect on the odds of late stage at diagnosis for women diagnosed
with breast cancer in NZ. There was also no trend to increasing odds with
increasing rurality or distance.
Table 3 shows the results of Cox Proportional Hazards
Regression. There was no statistically significant effect associated with place
of residence, except for those women living 51–100 km distant from a
cancer centre, who appeared to have better survival. This isolated finding is
dubious, particularly as it is unsupported by a trend to better or worse
survival amongst the other distances.
Table 2. Odds ratios for late stage diagnosis
by residence in urban and rural area
Table 3. Hazard ratios by residence in urban
and rural area
DiscussionThe results of this study show that urban/rural residence,
however classified, does not affect stage at diagnosis, or survival for women
with breast cancer in NZ. This suggests that access to, and effectiveness of
screening services, primary care, and specialist cancer services is equitable
regardless of whether women live in cities, towns, or rural areas. However it is
noted that stage at diagnosis and survival do not solely relate to
access/effectiveness of care. For example, a low-grade tumour is more likely to
be diagnosed at an early stage regardless the timeliness or effectiveness of
care.
Previous cancer research in NZ that has included a
geographic analysis has similarly not found differences in stage at diagnosis or
survival by urban/rural residence. Armstrong and Borman found no difference in
stage of breast cancer by urban/rural group for either Māori or
non-Māori women.15 Gill and Martin found
that increasing distance from cancer centre was not associated with poorer
survival from upper gastrointestinal cancer.16
Our study, which used three different measures of urban/rural residence, is
consistent with this previous research.
Several factors may explain why urban/rural residence does
not affect breast cancer stage at diagnosis. The nationally coordinated breast
screening programme (BreastScreen Aotearoa: BSA) encourages equitable screening
for rural and urban women. BSA has mobile/outreach services, and is accompanied
by stringent quality standards that help to ensure quality and consistency
throughout the country.26
Equitable access to early diagnosis of breast cancer in
primary care for both urban and rural women is supported by the existence of
formal guidelines for early diagnosis of breast cancer in primary
care.27 Furthermore the natural history of most
breast cancers is relatively indolent,28
meaning that any small delay in detection of breast cancer for rural women would
be unlikely to substantially affect the stage at diagnosis. Superimposed on
these factors, is the very high awareness of breast cancer in the community
(arising from strong public health messages, the popular media, and
women’s health advocacy groups) which is likely to prompt both rural and
urban women to seek early medical advice for breast complaints.
The lack of urban/rural difference in survival for women
with breast cancer may also be explained by a number of factors. Specialist
cancer services are configured in a way that attempts to balance centralisation
with local access. The six regional cancer centres provide overall regional
coordination, as well as providing clinics in hospitals outside their main
centre. So while initial oncology appointments and radiotherapy must be done at
the main centre, follow-up appointments and chemotherapy may be done at
peripheral hospitals.29
Furthermore, geographic distances that must be covered to
reach a major hospital (for cancer treatment) are not as vast in New Zealand as
in some countries in which survival differences have been found (e.g.
Australia).8 Non-governmental organisations
(such as the Cancer Society) also work hard to ensure that assistance is
available to support rural women to be able to attend specialist treatment (e.g.
volunteer drivers, petrol vouchers).
There are some acknowledged limitations to this study. For a
very small percentage of rural addresses, the automated domicile coding software
can have difficulty assigning a domicile code. For example, a non-specific rural
address (such as R.D. 2) may be geocoded to the rural mail delivery centre of
the nearest urban area, which will have an urban domicile code. Thus a small
number of rural cases may have been categorised into an urban group, possibly
leading to a slight underestimation of the effect of rural residence on stage at
diagnosis/survival.30
A second limitation is that we analysed deaths from all
causes in the survival analysis, rather than just breast cancer deaths. Given
that breast cancer is on average a relatively slowly progressive cancer that
predominantly affects middle to older aged women, the amount of 'noise' from
non-breast cancer related deaths may be significant in the survival analysis.
Lead time bias may also have influenced survival times, particularly as women in
the age-range eligible for screening (50–64 years during the time of this
study) were more likely to have their cancer detected earlier than those
ineligible for screening.
Finally, the time frame of this study is limited, and the
cohort of women diagnosed in 2002 will only have had four years of follow up. It
may be useful to re-analyse survival data at a later date.
ConclusionThis study did not show an urban/rural disparity in stage at
diagnosis or survival for women with breast cancer in NZ. The results may assist
policy-makers in deciding where to focus resources for breast cancer in the
future. Since urban/rural residence does not appear to have a major influence,
resources could perhaps be directed toward other factors, such as ethnicity,
which are known to affect stage at diagnosis and survival for women with breast
cancer in NZ.22
Competing interests: None.
Author information: Hayley Bennett, Public
Health Medicine Registrar, Australasian Faculty of Public Health Medicine,
Hamilton; Roger Marshall, Biostatistician, School of Population Health,
University of Auckland, Auckland; Ian Campbell, Breast and General Surgeon,
Senior Lecturer, Waikato District Health Board, Hamilton; Ross Lawrenson,
Professor and Head of Waikato Clinical School, University of Auckland,
Hamilton
Acknowledgement: The Ministry of
Health’s New Zealand Health Information Service (NZHIS) is acknowledged as
the source of the NZCR data.
Correspondence: Dr Hayley Bennett, Public
Health Medicine Registrar, 46 Casey Avenue, Hamilton. Email: hayleyandcam@clear.net.nz
References:
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