Purpose: This study aims to investigate the factors that influence the risk of metastatic relapse in women presenting with stage I-III breast cancer in New Zealand.
Methods: The study included women diagnosed with stage I-III breast cancer. Cumulative incidence of distant metastatic relapse was examined with the Kaplan-Meier method by cancer stage and subtype. Cox proportional hazards models were used to estimate the adjusted hazard ratio of developing recurrent metastatic breast cancer by cancer stage and biomarker subtype after adjustment for other factors.
Results: A total of 17,543 eligible women were identified. The 5-year cumulative incidence of metastatic recurrence was 3.7% for stage I, 13.3% for stage II and 30.9% for stage III disease. The adjusted hazard ratios (HR) of stage II and stage III breast cancer developing metastatic disease were 2.07 and 4.82 compared to stage I. The adjusted risk of distant metastatic relapse was highest for luminal B HER2- cancers (adjusted HR: 1.59 compared to luminal A disease). Higher grade cancers were associated with a higher risk of metastases. After adjustment, women aged 60-69 years and Asian women had the lowest risk of distant metastatic relapse.
Conclusions: The prognosis of women with locally invasive breast cancer differs greatly with the chance of developing metastatic disease depending on the stage of disease at diagnosis and the subtype. Grade of disease at diagnosis was also important. Māori or Pacific ethnicity did not influence the risk of developing metastatic disease, although Asian women seemed less likely to develop metastases.
Keywords: Biomarker subtype; Breast cancer; Cancer stage; Metastatic relapse.