Maori women more likely to get breast cancer: study

Research suggests Maori women are more likely to get breast cancer than European, Asian or Pacific women. Photo / Supplied

A "surprising" new study showing Maori women have the highest and fastest growing rates of breast cancer in New Zealand has raised questions about the causes of the deadly disease.

Research released by the University of Otago in Wellington today found the incidence of breast cancer among Maori had increased about 70 per cent between the periods 1981-1986 and 2001-2004, compared to about 50 per cent for European, Pacific and Asian women.

The rate of breast cancer in Maori women increased from 123 to 210 per 10,000 women, while for European women it rose from 114 to 170.

Study leader Dr Ruth Cunningham said that finding was hard to explain as Maori women traditionally gave birth earlier, had more children and took less advantage of breast cancer screening.

She could find no reason for the gulf in cancer rates between Maori and Pacific populations, which have a comparable birth rate and socioeconomic profile.

Similar international studies have found African-American women in the US and Aboriginal women in Australia both have lower rates than women of European descent, she said.

"It's very surprising given the results of international studies what we know as the causes of breast cancer. It raises the most questions. It prompts the most research. No factor we can find seems to be enough to explain it.

"Given what we know, one would expect Maori to have lower rates than European women as they give birth earlier, have more children and lower rates of hormone therapy use. All these factors normally reduce breast cancer rates."

Dr Cunningham said post-menopausal obesity could be one reason for the increased rate among Maori women.

It was possible there was an underlying genetic predisposition to breast cancer among Maori women, though more research needed to be done on the issue, she said.

"It would be premature to suggest that at this stage.

"It's likely that there are environmental factors not yet determined which are contributing to the differences in rates," she said.

She called on Maori women between the ages of 45 and 69 to get regular breast screening.

"Historically there has been a real difference in screening coverage for Maori women. They have a higher death rate from breast cancer, partly to do with the increased incidence, but also because many aren't surviving it."

The study showed Asian and Pacific women had the lowest incidence of breast cancer in New Zealand, with rates rising from 70 to 126 per 10,000 and 112 to 141 respectively.

The Asian breast cancer rate, while the lowest in the study, was high when compared to most Asian countries, suggesting environmental factors were having an impact, Dr Cunningham said.

Low Pacific rates were consistent with reduced risk factors such as having more children at a younger age and lower alcohol consumption.

Women from high socioeconomic groups were found to be more likely to get breast cancer than those from low socioeconomic groups because they had less children, were less likely to breast feed and more likely to use hormone therapy.

Breast cancer kills about 600 women a year.