296P - Investigating survival by breast cancer molecular subtype in Australia: A population-based study

Background

Survival rates across molecular subtypes of breast cancer (BC) have been reported, but these data do not reflect contemporary cohorts receiving newer BC treatments. We aimed to examine BC survival by subtype and stage of disease in a contemporary cohort of Australian women.

Methods

Cancer registry data of all invasive BC cases diagnosed between 2017-19 in Queensland, Australia, were included in the study and followed up to Feb 17, 2024, for overall survival (OS) and up to Dec 31, 2021, for BC-specific survival (BCSS). Molecular subtypes were based on hormone receptor (HR) and HER2 status classified into HR+/HER2-, HR+/HER2+, HR-/HER2+, and triple-negative BC (TNBC). Four-year OS and two-year BCSS by subtype were estimated. Crude survival rates were calculated by the Kaplan-Meier method. Flexible parametric survival models were used to calculate the adjusted hazard ratio.

Results

This study included 10,393 BC cases – 76% of cases were HR+/HER2- subtype, 5% HR+/HER+, 8.7% HR-/HER2+, and 10.3% TNBC. TNBC had the worst 4-year OS rate (78%) followed by HR-/HER2+ (87%), HR+/HER2- (89%), and HR+/HER2+ (90%). BCSS at 2-year was lowest for TNBC (87%) followed by HR-/HER2+ (93%), HR+/HER2+ (95%), and HR+/HER2- (97%). Compared to women with HR+/HER2- subtype, TNBC and HR-/HER2+ were more likely to die from any cause at 2-year post-diagnosis (TNBC: adjusted Hazard Ratio (HRadj)=2.42, 95%CI: 2.05-2.85; HR-/HER2+: HRadj=1.51, 95%CI: 1.14-1.74). These associations were attenuated at 4-years post-diagnosis with only the association in TNBC remaining significant (HRadj=1.42, 95%CI: 1.15-1.74). When stratified by stage, women with TNBC experienced significantly poorer BCSS at 2-year for Stages I-III (HRadj >7 for all stages, compared to HR+/HER2, but did not significantly differ for women with Stage IV BC.

Conclusions

TNBC continues to have markedly poorer survival outcomes in the first years after diagnosis, even in those with early-stage BC. Compared to earlier population-based studies, survival in those with HER2+ BC appear to have improved, although remains lower than HR+/HER2- BC. Further research for targeted treatments for TNBC, continues to be warranted.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

The University of Queensland (PhD scholarship).

Disclosure

All authors have declared no conflicts of interest.