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May 2005, Vol 95, No. 5 | American Journal of Public Health 834-837
© 2005 American Public Health Association
DOI: 10.2105/AJPH.2004.053678

RESEARCH AND PRACTICE

Ethnic Inequalities in Cancer Survival in New Zealand: Linkage Study

Mona Jeffreys, PhD, Vladimir Stevanovic, MD, Martin Tobias, MBBCh, FAFPHM, Chris Lewis, BSc(Hons), Lis Ellison-Loschmann, PhD, Neil Pearce, PhD, DSc and Tony Blakely, PhD

Mona Jeffreys, Lis Ellison-Loschmann, and Neil Pearce are with the Centre for Public Health Research, Massey University, Wellington, New Zealand. Vladimir Stevanovic and Chris Lewis are with the New Zealand Health Information Service, Wellington. Martin Tobias is with the Public Health Intelligence, Ministry of Health, Wellington. Tony Blakely is with the Department of Public Health, Wellington School of Medicine and Health Sciences, University of Otago, Wellington.

Correspondence: Requests for reprints should be sent to Mona Jeffreys, PhD, Centre for Public Health Research, Massey University, Private Bag 756, Wellington, New Zealand (e-mail: m.jeffreys{at}massey.ac.nz).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 References
 

We explored the contribution of stage at diagnosis to ethnic disparities in cancer survival in New Zealand. We linked 115811 adult patients with invasive cancer registered on the cancer registry (1994 to 2002) to mortality data. Age-standardized, 5-year relative survival rates were lowest for Maori, intermediate for Pacific people (otherwise known as Pacific Islanders), and highest for non-Maori/non-Pacific people for many cancers. Stage at diagnosis accounted for only part of these differences. Possible factors responsible for ethnic inequalities might include access to specialized cancer services and the quality of care received.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 References
 
The ethnic mix of the more than 4 million people of New Zealand includes the indigenous Maori (15% of the population) and Pacific Islanders (7%), originally from the South Pacific islands (hereafter referred to as Pacific people). The majority of non-Maori/non-Pacific people are of European descent. The Treaty of Waitangi (1840) was a formal agreement between Maori hapu (subtribes) and the British Crown, which guaranteed equity between Maori and other New Zealand citizens.1 Because health rights are implicit in the treaty,2 the poor health status of Maori3 can be considered a breach of their rights under the treaty.4

Since 1980, ethnic disparities in cancer mortality have widened.5 These inequalities cannot be explained by the differences in incidence6,7 and point to likely differences in access to and quality of health care.8 The few studies that have examined ethnic inequalities in cancer survival in New Zealand9–11 did not account for background (other cause) mortality rates. Our goal was to quantify the disparities and to estimate the magnitude of the contribution of stage of disease to these inequalities.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 References
 
Adult patients (aged 15 to 99 years) who had a cancer registered in the New Zealand Cancer Registry between July 1, 1994, and June 30, 2002, were identified (n = 124 599). We restricted the analyses to 20 main sites (n= 118188) and excluded patients with (1) death certificate only registrations (n = 2345, 2.0%), (2) in situ cancer (n = 7, < 0.1%), or (3) a home address overseas (n = 25, < 0.1%).

We used the National Health Index, which uniquely identifies health care users, to obtain mortality data to June 2003. We used a Maori, Pacific, non-Maori/non-Pacific–prioritized system of assigning ethnicity12 that is based on hospitalization and health administration data, as is standard in New Zealand. Patients with missing ethnicity data (2.6%) were analyzed with the non-Maori/non-Pacific group.

We used SURV3 software13 to estimate relative survival rates (RSRs)14 and standard errors15,16 based on ethnic-specific life tables by single year of age (15 to 99 years) from the 1996 census. Survival probabilities were estimated at yearly intervals.

RSRs were directly standardized first for age (15–44, 45–54, 55–64, 65–74, and 75–99 years) and then for disease stage (local, regional, distant spread).17 Pacific people were omitted from stage-standardized analyses because of their small numbers. We compared the age-standardized to the age- and stage-standardized Maori to non-Maori/non-Pacific RSR ratio to determine the contribution of stage to the survival inequalities.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 References
 
Among 115 811 patients, site-specific 5-year RSRs (Table 1Go) showed lower survival for Maori than for non-Maori/non-Pacific people at many sites, including cancer of the breast, cervix, colon/rectum, lung, prostate, and uterus. Ovarian cancer survival was higher in Maori compared with non-Maori/non-Pacific women. Survival among Pacific people was lower than non-Maori/non-Pacific people for colorectal, breast, and cervical cancer and higher for lung cancer. There were no differences by gender (results not shown).


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  		TABLE 1— Age-Standardized 5-Year Relative Survival Rates (RSR), by Ethnicity and Cancer Site: New Zealand, 1994 to 2002
 
The survival pattern among the patients with missing stage data (35%) differed by site, but age-standardized RSRs were similar between the total population and those patients with recorded stage data (Tables 1Go and 2Go). Following standardization for stage, the RSRs for Maori and non-Maori/non-Pacific people were close for cancers of the breast and prostate. However, stage at diagnosis explained little of the survival disparities for cancers of the bladder, cervix, colorectum, head/neck/larynx, lung, or uterus. The apparent survival advantage among Maori for ovarian cancer was fully explained by stage.


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  		TABLE 2— Age- and Age- and Stage-Standardized 5-Year Relative Survival Rates (RSR), by Ethnicity and Cancer Site: New Zealand, 1994 to 2002
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
References
 
Stage at diagnosis explains some but not all of the ethnic differences in cancer survival in New Zealand. Residual confounding through inaccuracies in stage classification could explain some of the results. Although little bias appears to have been introduced through exclusion of people with missing stage data. Differential access to health services and health system factors are likely to contribute to the remaining disparities.

Because cancer and death registration are mandatory, selective underascertainment is unlikely to explain the results. Using prioritized ethnicity, misclassification of Maori and Pacific ethnicity19 would underestimate the differences in survival between ethnic groups. Selective migration of terminally ill Pacific cancer patients to the Pacific would artificially inflate their survival rate, which may explain some of our results. Higher comorbidities in Maori, which could limit treatment options, might account for some of the observed differences.

Biological or genetic differences cannot account for ethnic differences in health.20 The unequal distribution of socioeconomic position by ethnicity may explain some, but probably not all,21–23 of the survival differences. In the United States, similar outcomes are experienced by people of different ethnicities in equal-access settings24; in other settings, the quality of cancer treatment differs by ethnicity.8 Health care utilization by Maori is not proportional to the expected need,3 which suggests that Maori are medically under-served in New Zealand.25 Factors that influence the receipt of optimal health care include cost,26 access through the secondary care system,27,28 rurality,10 and cultural safety,29 including perceived attitudes of health workers and acceptability of health providers to Maori.3,28 Maori-led health services may provide more acceptable opportunities for appropriate care for some Maori.30

To tackle these documented inequalities, it is necessary to pinpoint where on the cancer continuum inequalities arise. Survival disparities also could be reduced by addressing structural and service barriers within the health sector and by ensuring a commitment, with sufficient funding, to strengthen the Maori and Pacific health workforces.


   Acknowledgments
 
We gratefully acknowledge the financial support of the Lottery Health Research, who funded the salary for 1 of us (MJ) to carry out this work (grant AP102396). The Centre for Public Health Research is supported by a programme grant from the Health Research Council of New Zealand.

We are indebted to the hard work of staff at the New Zealand Cancer Registry.

Note. Neither Lottery Health Research nor the Health Research Council of New Zealand had any involvement in the data collection, analysis, or writing of the brief.

Human Participant Protection
Formal protocol approval was not sought because the study involved only anonymous linkage between 2 databases.


   Footnotes
 
Peer Reviewed

Contributors
M. Jeffreys, V. Stevanovic, and N. Pearce developed the study. C. Lewis and V. Stevanovic performed the linkage. V. Stevanovic and M. Jeffreys performed the data analyses. T. Blakely, M. Tobias, V. Stevanovic, and M. Jeffreys participated in initial discussions of the results. M. Jeffreys wrote the first draft. All authors contributed to subsequent drafts and the final brief. The discussions of indigenous health were contributed primarily by L. Ellison-Loschmann.

Accepted for publication December 11, 2004.


   References
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 References
 
1. Durie M. Whaiora: Maori Health Development. Auckland, New Zealand: Oxford University Press; 1994.

2. Durie MH. Te mana Te Kawanatanga: The Politics of Maori Self-Determination. Auckland, New Zealand: Oxford University Press; 1998.

3. Pomare E, Keefe-Ormsby V, Ormsby C, et al. Hauora. Maori Standards of Health III. A Study of the Years 1970–1991. Wellington, New Zealand: Te Ropu Rangahau Hauora a Eru Pomare; 1995.

4. Robson B, Reid P. Ethnicity Matters: Maori Perspectives. Review of the Measurement of Ethnicity. Wellington, New Zealand: Statistics New Zealand; 2001.

5. Ajwani S, Blakely T, Robson B, Tobias M, Bonne M. Decades of Disparity: Ethnic Mortality Trends in New Zealand 1980–1999. Wellington, New Zealand: Ministry of Health and University of Otago; 2003.

6. New Zealand Ministry of Health. Cancer in New Zealand: Trends and Projections. Wellington, New Zealand: New Zealand Ministry of Health; 2002. Public Health Intelligence Occasional Bulletin No. 15.

7. Foliaki S, Jeffreys M, Wright C, Blakey K, Pearce N. Cancer in Pacific people in New Zealand: a descriptive study. Pac Health Dialog. 2005. In press.

8. Smedley B, Stith A, Nelson A, eds. Unequal Treatment: Confronting Racial and Ethnic Disparities in Health Care. Washington, DC: National Academy Press; 2002.

9. Lethaby AE, Mason BH, Holdaway IM, Kay RG. Age and ethnicity as prognostic factors influencing overall survival in breast cancer patients in the Auckland region. Auckland Breast Cancer Study Group. N Z Med J. 1992;105(947):485–488.[Medline]

10. Gill AJ, Martin IG. Survival from upper gastrointestinal cancer in New Zealand: The effect of distance from a major hospital, socioeconomic status, ethnicity, age and gender. ANZ J Surg. 2002;72:643–646.[CrossRef][Medline]

11. Phillips AR, Lawes CM, Cooper GJ, Windsor JA. Ethnic disparity of pancreatic cancer in New Zealand. Int J Gastrointest Cancer. 2002;31(1–3):137–145.[Medline]

12. New Zealand Department of Statistics. Ethnicity in New Zealand: Recommendations for a Standard Classification. Discussion paper. Wellington, New Zealand: New Zealand Department of Statistics; 1990.

13. Dickman P, Hakulinen T, Voutilainen E. SURV3: Relative Survival Analysis [computer program]. v3.00. Helsinki, Finland: Finnish Cancer Registry; 2002.

14. Esteve J, Benhamou E, Croasdale M, Raymond L. Relative survival and the estimation of net survival: elements for further discussion. Stat Med. 1990;9: 529–538.[ISI][Medline]

15. Greenwood M. The Natural Duration of Cancer. London, England: HMSO; 1926. Report on Public Health and Medical Subjects No. 33

16. Capocaccia R, Gatta G, Roazzi P, et al. The EUROCARE-3 database: methodology of data collection, standardisation, quality control and statistical analysis. Ann Oncol. 2003;14(suppl 5):v14–v27.[Medline]

17. Young JL Jr, Roffers SD, Ries LAG, Fritz AG, Hurlbut AA, eds. SEER Summary Staging Manual—2000: Codes and Coding Instructions. Bethesda, MD: National Cancer Institute; 2001. NIH Pub. No. 01–4969.

18. International Classification of Diseases, 10th Revision. Geneva, Switzerland: World Health Organization; 1992.

19. Ajwani S, Blakely T, Robson B, Atkinson J, Kiro C. Unlocking the numerator-denominator bias III: adjustment ratios by ethnicity for 1981–1999 mortality data. The New Zealand Census-Mortality Study. N Z Med J. 2003;116(1175):U456.[Medline]

20. Pearce N, Foliaki S, Sporle A, Cunningham C. Genetics, race, ethnicity and health. BMJ. 2004;328: 1070–1072.[Free Full Text]

21. Pearce N, Pomare E, Marshall S, Borman B. Mortality and social class in Maori and non-Maori New Zealand men: changes between 1975–7 and 1985–7. N Z Med J. 1993;106:193–196.[ISI][Medline]

22. Salmond C, Crampton P. Deprivation and Health. In: Howden-Chapman PTM, ed. Social Inequalities in Health: New Zealand 1999. Wellington, New Zealand: Ministry of Health; 2000:9–64.

23. Blakely T, Kiro C, Woodward A. Unlocking the numerator-denominator bias. II: Adjustments to mortality rates by ethnicity and deprivation during 1991–94. The New Zealand Census-Mortality Study. N Z Med J. 2002;115(1147):43–48.[ISI][Medline]

24. Shavers VL, Brown ML. Racial and ethnic disparities in the receipt of cancer treatment. J Natl Cancer Inst. 2002;94:334–357.[Abstract/Free Full Text]

25. Malcolm L. Inequities in access to and utilisation of primary medical care services for Maori and low income New Zealanders. N Z Med J. 1996;109(1030): 356–358.[Medline]

26. Schoen C, Blendon R, DesRoches C, Osborn R, Doty M, Downey D. New Zealand Adults’ Health Care System Views and Experiences, 2001. Findings From the Commonwealth Fund 2001 International Health Policy Survey. New York, NY: The Commonwealth Fund; 2002. Report No. 553.

27. Baxter J. Eight Health Gain Priority Areas for Maori Health. Report 1: Mental Health. A Report Prepared for the Maori Health Group, Health Funding Authority. Auckland, New Zealand: Health Funding Authority; 2000.

28. Baxter J. Barriers to Health Care for Maori with Known Diabetes: A Literature Review and Summary of Issues. Wellington, New Zealand: New Zealand National Working Group on Diabetes; 2002.

29. Trans-HHS Cancer Health Disparities Progress Review Group. Making Cancer Health Disparities History. Washington, DC: US Department of Health and Human Services; 2004.

30. Ellison-Loschmann L, Pearce N. He Mate Huango: an update on Maori asthma. Pac Health Dialog. 2000; 7:82–93.[Medline]




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