Treatment and survival of Asian women diagnosed with breast cancer in New Zealand
Chunhuan Lao, Ross Lawrenson, Melissa Edwards and Ian Campbell
This study aims to examine the differences in characteristics, treatment and survival between Asian and European women diagnosed with stage I–III breast cancer in New Zealand.
The studied population included European women and Asian women diagnosed with stage I–III breast cancer between June 2000 and May 2013 identified from the combined Waikato and Auckland Breast Cancer Registers. Characteristics and treatment were compared between Asian and European women. Kaplan–Meier method was used to examine the
survival difference. Cox proportional hazards model was used to estimate the hazard ratio (HR) of mortality.
The studied cohort included 8608 European and 949 Asian women. Asian women were younger, had less comorbidities and were less likely to be obese than European women. Asian women were more likely to have grade 3, larger and HER2+ breast cancers. Asian women were more likely to receive mastectomy, less likely to have reconstruction after mastectomy, less likely to have chemotherapy, less likely to be treated with trastuzumab if HER2+, and had better adherence to endocrine therapy (adjusted odds ratio: 1.54; 95% CI 1.22–1.93). Asian women had better cancer-specific survival and all-cause survival than European women. The adjusted HR of cancer-specific mortality and all-cause mortality were 0.64 (95% CI 0.49–0.82) and 0.68 (95% CI 0.55–0.84), respectively.
Asian women are more likely to have high grade, larger and HER2+ breast cancers than European women. In spite of this, they had better breast cancer outcomes. Possible explanations include the differences in adherence to endocrine therapy, age, BMI and comorbidities.
Outcomes in different ethnic groups of New Zealand patients with screen-detected vs. non-screen detected breast cancer.
Ross Lawrenson, Chunhuan Lao, Gregory Jacobson, Sanjeewa Seneviratne, Nina Scott, Diana Sarfati, Mark Elwood and Ian Campbell
To compare characteristics and survival of New Zealand European, Māori, and Pacific women with screen-detected vs. non-screen-detected breast cancer.
Women aged 45-69 diagnosed with invasive breast cancer between January 2005 and May 2013 were identified from the Waikato and Auckland Breast Cancer Registries. Patient demographics and tumour characteristics were described by detection mode and ethnicity. Kaplan-Meier method was used to estimate the five-year breast cancer-specific survival of women with stage I-III breast cancer by ethnicity and detection mode.
Women with screen-detected cancers were older, had smaller tumours, fewer stage IV (0.8% vs. 7.6%), fewer high grade (16.8% vs. 39.0%), and fewer lymph node positive diseases (26.3% vs. 51.5%) than women with non-screen-detected cancers. There were more Luminal A (70.0% vs. 54.0%), fewer human epidermal growth factor receptor 2 positive non-Luminal (4.4% vs. 8.8%), and fewer triple negative cases (7.0% vs. 13.8%) in screen-detected than non-screen-detected cancers. If not screen detected, 22.7% of breast cancers in Pacific women were stage IV compared with 2.4% if screen detected. If not screen detected, the five-year breast cancer-specific survival was 91.1% for New Zealand European women, 84.2% for Māori women, and 80.2% for Pacific women (p-value <0.001). For screen-detected breast cancer, survival between different ethnic groups was similar.
Breast cancers detected through screening are diagnosed at an earlier stage and have a greater proportion of subtypes, with better outcome. Variations in survival for Māori and Pacific women are only found in women with non-screen-detected breast cancer.
The impact of different tumor subtypes on management and survival of New Zealand women with Stage I-III breast cancer.
Ross Lawrenson, Chunhuan Lao, Ian Campbell, Vernon Harvey, Sanjeewa Seneviratne, Mark Elwood, Diana Sarfati, Marion Kuper-Hommel
This study aims to describe the prevalence and characteristics of the different ER/PR/HER2 subtypes in New Zealand women with breast cancer, and to explore their treatment and outcomes.
This study included women diagnosed with Stage I–III breast cancer between January 2006 and May 2013, recorded in the combined Waikato and Auckland Breast Cancer Registers, and with complete data on their ER, PR and HER2 status. Five ER/PR/HER2 phenotypes were classified. Kaplan-Meier method and Cox proportional hazards model were used to examine the survival differences among these subtypes.
Of the 6,875 eligible women, 4,274 (62.2%) were classified as Luminal A, 836 (12.2%) as Luminal B HER2-, 605 (8.8%) as Luminal B HER2+, 401 (5.8%) as HER2+ non-Luminal and 759 (11.0%) as Triple Negative. Maori and Pacific women were less likely to have Triple Negative disease, while Pacific women were more likely to be HER2+ non-Luminal. The five-year breast cancer-specific survival was worst for HER2+ non-Luminal (80.1%) and Triple Negative (81.9%), followed by Luminal B HER2- (89.3%) and Luminal B HER2+ (91.6%), and was the best for Luminal A (96.8%). The adjusted breast cancer-specific mortality hazard ratio for Triple Negative and HER2+ non-Luminal compared to Luminal A was 4.91 (95% CI: .86–6.26) and 3.94 (95% CI: 2.94–5.30), respectively.
The pattern of phenotype in women with Stage I-III breast cancer is similar to the overseas cohorts. Most New Zealand women with Luminal A breast cancer have a very good prognosis, but the less common subtypes have relatively poor outcomes.
Surgical treatment of early stage breast cancer in Auckland and Waikato regions of New Zealand
Ian Campbell, Chunhuan Lao, Tania Blackmore, Melissa Edwards, Louise Hayes, Alex Ng and Ross Lawrenson
The aim of this study was to understand the factors influencing the use of surgical options by New Zealand wāhine/women with newly diagnosed breast cancer.
Using data from the Auckland and Waikato breast cancer registers, 11, 798 women diagnosed with stage I-III breast cancer from June 2000 to May 2013 were included. The characteristics of women receiving different surgical treatments and having immediate breast reconstruction following mastectomy were examined. A logistic regression was used to estimate the odds ratio of having breast-conserving surgery (BCS) versus mastectomy and immediate post-mastectomy reconstruction. Bilateral breast cancer cases and women with unilateral breast cancer, but who had bilateral surgery, were also identified.
Fifty‐two percent of women received BCS and 44% had mastectomy over the study period. Key influences associated with BCS were age, mode of diagnosis, socio‐economic status and public or private treatment. Just under half of the women who underwent bilateral surgery did not have bilateral cancer. Nineteen percent of women undergoing mastectomy underwent immediate reconstruction. Implant use increased slightly over the study period but there was a decrease in the use of autologous flap procedures.
Surgical management of women with localized breast cancer was generally in line with guidelines, but with potential to further increase the use of breast conservation and immediate reconstruction in suitable cases.
Development and validation of a new predictive model for breast cancer survival in New Zealand and comparison to the Nottingham prognostic index
Mark Elwood, Essa Tawfiq, Sandar Tin Tin, Roger J. Marshall, Tung M. Phung, Ian Campbell, Vernon Harvey and Ross Lawrenson
The only available predictive models for the outcome of breast cancer patients in New Zealand (NZ) are based on data in other countries. We aimed to develop and validate a predictive model using NZ data for this population, and compare its performance to a widely used overseas model, the Nottingham Prognostic Index (NPI).
We developed a model to predict 10-year breast cancer-specific survival, using data collected prospectively in the largest population-based regional breast cancer registry in NZ (Auckland, 9182 patients), and assessed its performance in this data set (internal validation) and in an independent NZ population-based series of 2625 patients in Waikato (external validation). The data included all women with primary invasive breast cancer diagnosed from 1 June 2000 to 30 June 2014, with follow up to death or Dec 31, 2014. We used multivariate Cox proportional hazards regression to assess predictors and to calculate predicted 10-year breast cancer mortality, and therefore survival, probability for each patient. We assessed observed survival by the Kaplan Meier method. We assessed discrimination by the C statistic, and calibration by comparing predicted and observed survival rates for patients in 10 groups ordered by predicted 10-year survival. We compared this NZ model with the Nottingham Prognostic Index (NPI) in this validation data set.
Discrimination was good: C statistics were 0.84 for internal validity and 0.83 for an independent external validity. For calibration, for both internal and external validity the predicted 10-year survival probabilities in all groups of patients, ordered by predicted survival, were within the 95% confidence intervals (CI) of the observed Kaplan-Meier survival probabilities. The NZ model showed good discrimination even within the prognostic groups defined by the NPI.
These results for the New Zealand model show good internal and external validity, transportability, and potential clinical value of the model, and its clear superiority over the NPI. Further research is needed to assess other potential predictors, to assess the model’s performance in specific subgroups of patients, and to compare it to other models, which have been developed in other countries and have not yet been tested in NZ.
Receipt of radiotherapy after mastectomy in women with breast cancer: Population-based cohart study in New Zealand
Phyu Mon Latt, Sandar Tin Tin, Mark Elwood, Ross Lawrenson and Ian Campbell
To investigate the receipt of postmastectomy radiotherapy (PMRT) in breast cancer patients in New Zealand for whom radiotherapy is strongly recommended in current clinical guidelines.
This study involved all women who were diagnosed with primary invasive breast cancer in two health regions, had undergone a mastectomy, and met the ‘strong recommendation’ criteria for PMRT based on New Zealand National Guidelines. We performed logistic regression analyses to identify demographic and clinical factors associated with the receipt of PMRT.
Of the 1,455 patients with stage II to III cancers included in this analysis, 1195 (82%) received radiotherapy. The receipt of PMRT decreased with increasing age, and was significantly lower in rural residents, Māori and Pacific women, those with more comorbidity, those who receive primary cancer care in the a public facility, and those diagnosed with stage III cancer. Although not significant, the receipt was also lower in patients who resided in more deprived neighborhood, and those with comorbidities. The findings restricted to stage III patients (n = 1325), and to those diagnosed since 2010 (n = 422), after the current guidelines were published, which were very similar to the whole cohort.
Disparities exist in the receipt of PMRT in breast cancer patients in New Zealand, underscoring the need for a greater equity focus in management of breast cancer.
Impact of radiotherapy on cardiovascular health of women with breast cancer
Ross Lawrenson, Chunhuan Lao, Ahmed Ali and Ian Campbell
This study aims to examine the impact of radiotherapy on the cardiovascular health of women diagnosed with breast cancer in the Waikato region in New Zealand.
Women diagnosed with stage 0–III breast cancer and recorded in the Waikato Breast Cancer Registry were divided into two groups: a radiotherapy group and a no-radiotherapy group. Baseline characteristics and treatments were compared in the two groups. Kaplan–Meier survival analysis was performed to compare cardiovascular morbidity and mortality. Cox Proportional Hazard regression analysis was used to estimate the hazard ratio of radiotherapy on the risk of cardiovascular morbidity and mortality while adjusting for other factors.
A total of 3528 women were included in this study, with 2303 in the radiotherapy group and 1225 in the no-radiotherapy group. At 10-year followup, 11.7% of women in the radiotherapy group and 19.4% in the no-radiotherapy group experienced cardiovascular events. Only 2.3% of patients who received radiotherapy died of cardiovascular disease by 10 years compared to 7.0% in the no-radiotherapy group. After adjusting for clinically significant factors, there was unexplained reduced risk of developing cardiovascular disease in the radiotherapy group compared to the no-radiotherapy group (HR 0.73, 95% CI: 0.59–0.92). No significant difference was found in cardiovascular mortality between the two groups.
Radiotherapy appears less likely to be offered to patients at higher risk of cardiovascular disease. No evidence of increased risk of a cardiovascular event was found in the group of women with breast cancer treated with radiotherapy and current regimens appear safe. Traditional cardiovascular risk factors remain the main culprits in this setting. Clinicians should work with patients in managing these risk factors for optimal results.
Ethnic disparities in breast cancer survival in New Zealand: which factors contribute?
Sandar Tin Tin, Mark Elwood, Charis Brown, Diana Sarfati, Ian Campbell, Nina Scott, Reena Ramsaroop, Sanjeewa Seneviratne, Vernon Harvey and Ross Lawrenson
New Zealand has major ethnic disparities in breast cancer survival with Māori (indigenous people) and Pacific women (immigrants or descended from immigrants from Pacific Islands) faring much worse than other ethnic groups. This paper identified underlying factors and assessed their relative contribution to this risk differential.
This study involved all women who were diagnosed with primary invasive breast cancer in two health regions, covering about 40% of the national population, between January 2000 and June 2014. Māori and Pacific patients were compared with other ethnic groups in terms of demographics, mode of diagnosis, disease factors and treatment factors. Cox regression modelling was performed with stepwise adjustments, and hazards of excess mortality from breast cancer for Māori and Pacific patients were assessed.
Of the 13,657 patients who were included in this analysis, 1281 (9.4%) were Māori, and 897 (6.6%) were Pacific women. Compared to other ethnic groups, they were younger, more likely to reside in deprived neighbourhoods and to have co-morbidities, and less likely to be diagnosed through screening and with early stage cancer, to be treated in a private care facility, to receive timely cancer treatment, and to receive breast conserving surgery. They had a higher risk of excess mortality from breast cancer (age and year of diagnosis adjusted hazard ratio: 1.76; 95% CI: 1.51–2.04 for Māori and 1.97; 95% CI: 1.67–2.32 for Pacific women), of which 75% and 99% respectively were explained by baseline differences. The most important contributor was late stage at diagnosis. Other contributors included neighbourhood deprivation, mode of diagnosis, type of health care facility where primary cancer treatment was undertaken and type of loco-regional therapy.
Late diagnosis, deprivation and differential access to and quality of cancer care services were the key contributors to ethnic disparities in breast cancer survival in New Zealand. Our findings underscore the need for a greater equity focus along the breast cancer care pathway, with an emphasis on improving access to early diagnosis for Māori and Pacific women.
Obesity and breast cancer outcomes in chemotherapy patients in New Zealand – a population-based cohort study
Mark Elwood, Sandar Tin Tin, Marion Kuper-Hommel, Ross Lawrenson and Ian Campbell
Obesity has been reported as an adverse prognostic factor in breast cancer, but inconsistently, and under-treatment with chemotherapy may occur. We provide the first assessment of obesity and breast cancer outcomes in a population-based, multi-ethnic cohort of New Zealand patients treated with chemotherapy.
All 3536 women diagnosed with invasive breast cancer in the Waikato region of New Zealand from 2000-2014 were registered and followed until last follow-up in specialist or primary care, death or Dec 2014; median follow-up 4.1 years. For the 1049 patients receiving chemotherapy, mortality from breast cancer, other causes, and all causes, and rates of loco-regional and of distant recurrence, were assessed by body mass index (BMI), recorded after diagnosis, adjusting for other clinico-pathological and demographic factors by Cox regression.
BMI was known for 98% (n=1049); 33% were overweight (BMI 25-29.9), 21% were obese (BMI 30-34.9), and 14% were very obese (BMI 35+). There were no significant associations between obesity and survival, after adjustment for demographic and clinical factors (hazard ratios, HR, for very obese compared to BMI 21-24, for breast cancer deaths 0.96 (0.56-1.67), and for all deaths 1.03 (0.63-1.67), respectively, and only small non-significant associations for loco-regional or metastatic recurrence rates (HR 1.17 and 1.33 respectively). Subgroup analyses by age, menopausal status, ethnicity, stage, post-surgical radiotherapy, mode of diagnosis, type of surgery, and receptor status, showed no associations. No associations were seen with BMI as a continuous variable. The results in all patients irrespective of treatment but with recorded BMI data (n=2296) showed similar results.
In this population, obesity assessed post-diagnosis had no effect on survival or recurrence, based on 1049 patients with chemotherapy treatment with follow-up up to 14 years.