Introduction

HER2 status has been routinely ascertained for stage I-III breast cancer since late 2005. Trastuzumab was first funded in New Zealand for use in HER2+ breast cancer in July 2007. This observational study aims to compare the difference in outcome between women with HER2+ stage I-III breast cancer who received trastuzumab as adjuvant therapy versus those who did not. Differences in presentation, treatment and outcomes between Māori and NZ European were studied.

Methods

The combined Waikato and Auckland Breast Cancer Registries have clinical details of 12377 women diagnosed with breast cancer between June 2000 and May 2013. 9506 women with breast cancer were tested for HER2 receptor status. Proportion of women with HER2+ (FISH amplified or IHC 3+), stage I-III breast cancer were examined by age, ethnicity and stage. Differences in use of trastuzumab for women with stage I-III breast cancer with a tumour size equal or larger than 1 cm and aged less than 75 years were assessed by ethnicity and year of diagnosis. Patients who had inflammatory breast cancer or developed metastatic disease or local recurrence within 3 months after diagnosis were excluded. Kaplan-Meier method and Cox proportional hazards model were used to examine the breast cancer-specific survival between women treated with trastuzumab and chemotherapy and those treated with chemotherapy without trastuzumab.

Results

1454 patients with early invasive breast cancer were HER2+. The proportion of cases with HER2+, stage I-III breast cancer increased with stage (stage I-III: 11.5%-26.9%), but decreased with age (<40 years to 80+ years: 28.8%-9.7%). Māori women were more likely to have HER2+ cancers than NZ European (17.8% versus 14.9%; p=0.02). Among the eligible patients, 605 women received trastuzumab and chemotherapy within 12 months for stage I-III breast cancer, and 275 had chemotherapy without trastuzumab. A small proportion (10.2%, 34/333) of women diagnosed in 2000-2005 received trastuzumab as part of a clinical trial. The proportion of women who received trastuzumab increased to 60.3% in 2006-2009 and to 87.1% in 2010-2013. 46.2% of Māori women were treated with trastuzumab compared to 55.9% of NZ European (p=0.040). The cancer-specific survival estimated with Kaplan-Meier method is shown in Table 1. Women treated with chemotherapy without trastuzumab were 2.7 times (95% CI: 1.9-3.9) more likely to die of breast cancer compared to those treated with trastuzumab and chemotherapy, after adjustment for stage, tumour size and hormone therapy.

Table 1. Breast cancer-specific survival between women with HER2+ stage I-III breast cancer who received trastuzumab as adjuvant therapy versus those who did not

Treatment Number of patients Median follow-up time (months) 5-year survival 10-year survival 
Trastuzumab+chemotherapy 605 53 89.6% 84.3% 
Chemotherapy without trastuzumab 275 107 75.6% 69.1% 
Treatment Number of patients Median follow-up time (months) 5-year survival 10-year survival 
Trastuzumab+chemotherapy 605 53 89.6% 84.3% 
Chemotherapy without trastuzumab 275 107 75.6% 69.1% 

Conclusions

Trastuzumab improved the breast cancer-specific survival of women with HER2+ stage I-III breast cancer. Māori women were more likely to have HER2+ cancer and less likely to be treated with trastuzumab. Rates of treatment with trastuzumab and the adjusted survival between Māori women and NZ European women were not significantly different.

Citation Format: Lawrenson R, Lao C, Harvey V, Campbell I, Brown C, Seneviratne S, Edwards M, Scott N, Elwood M, Sarfati D, Kuper-Hommel M. Trastuzumab improves outcomes of New Zealand women with HER2+ stage I-III breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-21-28.