# Urban Rural Differences in Breast Cancer in New Zealand
## 2 Methods  
The population for this study included all women diagnosed with invasive breast cancer in the Waikato and Auckland regions from June 2000 to May 2013. The two registers have been collecting data prospectively on newly diagnosed women with breast cancer and have accurate data on demographic characteristics including place of domicile as well as clinical data on the breast cancer at diagnosis and subsequent treatment. Ethical approval for this study was obtained from the New Zealand Northern \"A\" Health and Disability Ethics Committee (Ref. No. 12/NTA/42).  
The definition of urban and rural varies considerably across different studies and countries. Within NZ a number of different definitions have been considered [10; 11]. For this study we have taken the seven different classifications of the urban rural profile classification basis of NZ statistics which is based on both domicile and work place. The seven categories are Major Urban; Satellite Urban; Independent Urban; Rural with high urban influence; Rural with moderate urban influence; Rural with low urban influence and Highly Rural/Remote. We have categorised rural areas with high urban influence to be urban as these communities generally are the high socioeconomic population living close to urban centres where these families work, shop and receive health care. On the other hand the NZ independent urban centres are those independent towns where general practitioners are classified as being rural and receive a rural bonus. Consequently we have redefined urban as either a major or satellite urban community or communities of high urban influence. Rural we have considered to be independent urban communities or those designated rural with moderate or low or no urban influence.  
Other variables included in the study were: age (<40, 40-49, 50-59, 60-69, 70-79, 80+ years), ethnicity (NZ European, Maori, Pacific, Asian, others), cancer stage (I, II, III, IV), grade (1, 2, 3), tumour size (0-10, 10-20, 20-30, 30-50, 50+ mm), mode of detection (screen detected, not screen detected), and hormone status (Estrogen receptor (ER) and progesterone receptor (PR) negative, ER and/or PR positive). We first compared the characteristics between urban and rural women, and then compared urban and rural Maori and NZ European women. Key demographic and disease characteristics were described for the total cohort, for urban and rural populations and stratified by ethnicity.  
Mortality information including date of death and cause of death were from both the combined registers and the Mortality Collection in New Zealand. For all-cause survival analyses, patients without mortality information were considered to be censored on the last updated date for Mortality Collection which was 31 December 2014. For cancer-specific analyses, deaths from other causes were censored on the date of death. Cancer-specific and all-cause survival were assessed for rural and urban women at 5 and 10 years using Kaplan-Meier method. Models were fitted using Cox proportional hazards modelswith cancer-specific and all-cause deaths as outcomes of interests, to compare outcomes for rural compared with urban women for the whole cohort and stratified by ethnicity. The proportional hazards assumption was tested for both breast cancer-specific and total mortality by creating a time-dependent covariate as an interaction term between urban-rural residence and survival time. The survival difference between subgroups was considered significant if the \(p\)-value was less than 0.05. All data analyses were performed in SPSS (IBM Corporation, New York, NY, USA).