Investigating reasons for socioeconomic inequalities in breast cancer survival in New Zealand.
BACKGROUND
This study investigated the role that demographic and tumour factors play in explaining socioeconomic inequalities in breast cancer survival.


METHODS
Breast cancer cases notified to the New Zealand Cancer Registry (NZCR) from April 2005 to April 2007 were followed up to April 2009. The New Zealand area-based deprivation index (NZDep) was used as a measure of socioeconomic position. Relative survival rates were estimated using sex-, deprivation- and ethnic-specific life tables. Multiple imputation was used to impute missing data. Excess mortality modelling was used to estimate the contribution of demographic and tumour factors to inequalities in survival.


RESULTS
There were 2968 breast cancer cases included and 433 recorded deaths. Relative survival rates at 4 years varied across deprivation groups. Using NZDep deciles 1-4 (least deprived) as the reference group, the age- and ethnicity-adjusted hazard ratio (HR) for NZDep deciles 7-8 was 2.03 (CI 1.36-3.04) and for NZDep deciles 9-10 was 1.93 (CI 1.28-2.92). In the fully adjusted model there remained 50% excess mortality for the two most deprived groups compared to the most affluent. Variables which measured timely access to care (extent/size) accounted for more of the survival disparity than breast cancer subtype variables (ER/PR/HER2).


CONCLUSIONS
Women from deprived areas in New Zealand who are diagnosed with breast cancer are less likely to survive as long as those from affluent areas. A substantial proportion of these socioeconomic disparities can be attributed to differential access to health care although other factors, currently unknown, are also likely to play an important role.
McKenzie
Fiona
F
Centre for Public Health Research, Massey University, Private Bag 756, Wellington, New Zealand. f.j.mckenzie@massey.ac.nz
Ellison-Loschmann
Lis
L
Jeffreys
Mona
M
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000191:economics / Q000401:mortality* / Q000473:pathology; D005260:Female; D054624:Health Status Disparities; D006801:Humans; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D012042:Registries; D012307:Risk Factors; D012959:Socioeconomic Factors; D015996:Survival Rate