By Jean Balchin 15/12/2017

A recent study published in the New Zealand Medical Journal has revealed a number of differences between Pasifika women and New Zealand European women diagnosed with breast cancer in New Zealand. The team found that Pasifika women in New Zealand are more likely to be diagnosed with breast cancer when the disease is already relatively advanced.

The research team examined records of breast cancer diagnosis in Auckland and the Waikato between June 2000 and May 2013 and found that a third of Pasifika women had advanced disease at diagnosis compared to less than a fifth of Pākehā. Later diagnoses increases the risks of breast cancer. However, increased access to healthcare and ensuring all Pasifika women get screened at an appropriate time can cut the proportion of women diagnosed late.

Breast cancer in New Zealand

According to the Breast Cancer Foundation of New Zealand, breast cancer is the most common cancer for Kiwi women and the third most common cancer overall. One in eight New Zealand women are affected by breast cancer over their lifetime, and about 70% – 75% of women who are diagnosed with breast cancer and about 80% of women who die from it are aged 50 years or older.

Some women are at greater risk of breast cancer because there is a history of close family members having the disease.However, most women who develop breast cancer have no relatives with the disease. Even among women who do have relatives with breast cancer, most will never develop it. (Ministry of Health 2015)

While it is less common, young women can get breast cancer too. 6% of breast cancer in NZ occurs under the age of 40 years. Although it is uncommon, men also get breast cancer. About 25 men are diagnosed in New Zealand each year.

Breast cancer in New Zealand-based Pasifika women is a troublingly significant issue. Although there is a lower incidence of breast cancer in Pasifika women compared to New Zealand European women, they have higher breast cancer mortality and lower five-year survival.

The Breast Cancer Foundation of New Zealand.

Data on all Pasifika and New Zealand European women diagnosed with breast cancer (C50) during the period 1 June 2000 to 31 May 2013 was extracted from the Auckland and Waikato Breast Cancer Registries. Chi-square tests and Descriptive tables were drawn up to examine differences in characteristics and tumour biology between Pasifika and New Zealand European women. Factors that contributed to an increased risk of advanced stage at diagnosis were deduced by logistic regression.

The research team from University of Waikato, University of Auckland, and the University of Otago significantly higher proportion of Pasifika women had advanced disease at diagnosis compared to New Zealand European women at 33.3% and 18.3%, respectively.

Cancer biology in Pasifika women was more likely to be:

1) HER2+

According to the Dr Susan Love Foundation, HER2 is one of more than 100,000 genes found in the nucleus of all human cells. The HER2 gene helps cells grow, divide, and repair themselves. Every cell should have only two copies of the HER2 gene. If it has more than two copies (referred to as gene amplification), these extra genes result in there being too many HER2 protein receptors on the cancer cell’s surface (referred to as protein overexpression.) These receptors pick up more grow-and-divide messages than a cell should normally get, fueling the cancer’s growth.

2) ER/PR negative 

Estrogen receptors (ER) and progesterone receptors (PR; also called PgR) may be found in breast cancer cells. Cancer cells with these receptors depend on estrogen and related hormones, such as progesterone, to grow. Estrogen and progesterone influence many hormonal functions in women, such as breast development.

3) have a tumour size of >50mm.

If breast cancer cells have estrogen receptors, the cancer is called ER-positive breast cancer. If breast cancer cells have progesterone receptors, the cancer is called PR-positive breast cancer. If the cells do not have either of these two receptors, the cancer is called ER/PR-negative. About two-thirds of breast cancers are ER and/or PR positive.

Pasifika women live in higher deprivation areas of 9–10 compared to New Zealand European women (55% vs 14%, respectively) and were less likely to have their cancer identified through screening. Logistic regression showed that if Pasifika women were on the screen-detected pathway they had similar odds (not sig.) of having advanced disease at diagnosis to New Zealand European women.

For women of screening age, adherence to the screening programme and improvements in access to earlier diagnosis for Pasifika women under the current screening age have the potential to make a substantial difference in the number of Pasifika women presenting with late-stage disease.