Breast cancer is the most common cancer in New Zealand women, accounting for approximately 3000 new registrations per year, affecting one in nine women and resulting in more than 600 deaths annually. This study analysed data of patients selected with prognostic factor of Nottingham grade 3 tumours over a specified five- year period. These represent a heterogeneous group of cancers with variable survival rates.
All women diagnosed with Nottingham grade 3 invasive breast cancer between 1 st January 2011 to 31 st December 2015, from four Breast Cancer Registries in New Zealand (Auckland, Waikato, Christchurch, and Wellington) were studied.
Applying Fine-Gray analyses, the study of 2,493 women found that subjects in the older age group (>70 years) had a higher five-year mortality risk (SHR: 1.74 to 2.25, p: 0.053 to <0.001). Analysis of hormonal receptors showed that tumours with hormonal profile ER-positive, PR negative and ER-negative, PR negative subjects were at increased mortality risk (SHR: 3.56, p: <0.001) and (SHR: 2.67, p: <0.001) respectively. Molecular subtypes TNBC and Luminal B subjects were at increased risk of five-year mortality (SHR: 3.01 and 3.35 respectively, both p: <0.001). HER2 enriched subjects, were at elevated risk (SHR: 1.66, p: 0.11). Women identifying as NZ European ethnicity were at elevated risk of mortality overall (SHR: 1.70, p: 0.11), and they presented with the highest CIF across ethnicities. The NZ Europeans represented the largest proportion of HER2 enriched and TNBC subjects; however, Pacific Islanders experienced the highest HER2 CIF.
The survival rates for grade 3 breast cancer vary across the selected prognostic factors and ethnicity. Although grade 3 breast cancer is considered as high grade heterogeneous cancer, this study showed that not every patient has a poor outcome. NZ Europeans are worst affected followed by Pacific Islanders. Biology of the cancer and ethnicity needs to be looked at as a possible factor associated with this disease for survival differences. The results of this study make an initial contribution to the understanding of high-grade malignancy and other prognostic factors must be included in order to get a better understanding of survival differences.