The impact of different tumor subtypes on management and survival of New Zealand women with Stage I-III breast cancer

28 May 2018

Ross Lawrenson, Chunhuan Lao, Ian Campbell, Vernon Harvey, Sanjeewa Seneviratne, Mark Elwood, Diana Sarfati, Marion Kuper-Hommel

Aims
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.

Methods
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.

Results
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.

Conclusions
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.