Rapid Fire Oral Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2026

Lifestyle factors across generations and early-onset breast cancer risk: Evidence from the Australian Longitudinal Study on Women’s Health (142466)

Md Sohel Rana 1 2 , MD Mijanur Rahman 1 3 , Luke Marinovich 1 4 , Dominic Cavenagh 5 , Julie E. Byles 6 7 , Nehmat Houssami 1 4 , Xue Qin Yu 1
  1. The Daffodil Centre, The University of Sydney and Cancer Council NSW, Sydney, NSW, Australia
  2. Department of Statistics, Comilla University, Kotbari, Cumilla-3506, Bangladesh
  3. Collaboration for Cancer Outcomes, Research and Evaluation (CCORE), School of Clinical Medicine, Faculty of Medicine & Health, University of New South Wales, Sydney, NSW, Australia
  4. Sydney School of Public Health, Faculty of Medicine and Health, The University of Sydney, Camperdown, Sydney, NSW, Australia
  5. Centre for Women’s Health Research, University of Newcastle, Newcastle, NSW, Australia
  6. Hunter Medical Research Institute, New Lambton Heights, Newcastle, NSW, Australia
  7. University of Newcastle, Callaghan, Newcastle, NSW, Australia

Aims

Early-onset breast cancer (EOBC, diagnosed before age 50) often presents at an advanced stage. Generational changes in lifestyle and reproductive factors may be relevant to EOBC risk. This study investigated generational differences in these factors and their associations with EOBC incidence.

Methods

This study included women from two birth cohorts (1946-51 and 1973-78) in the Australian Longitudinal Study on Women’s Health, with EOBC identified via linkage to the Australian Cancer Database. Lifestyle, reproductive, and sociodemographic factors were compared at similar ages. In the younger cohort, Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for EOBC incidence, with lifestyle factors modelled as time‑varying exposures and adjusting for reproductive and sociodemographic factors.

Results

Compared to the 1946-51 birth cohort, women born in 1973-78 had a higher prevalence of risky/high-risk alcohol consumption (14.65% vs 5.27%), overweight/obesity (60.98% vs 45.49%) and higher educational attainment (55.70% vs 13.86%), but were less likely to be current smokers (9.35% vs 17.80%). They also had fewer children (e.g., nulliparous: 18.08% vs 6.11%) and were less likely to be partnered (71.67% vs 82.54%). In the younger cohort, alcohol consumption (HR [95%CI]: 1.47 [1.04-2.06]) and smoking (1.29 [1.09-1.53]) were associated with an increased hazard of EOBC.

Conclusions

Substantial generational changes in lifestyle, reproductive, and sociodemographic risk factors were observed. Smoking and alcohol consumption were associated with EOBC in the younger cohort. These findings suggest a potential relevance of changing risk profiles across generations but do not establish their contribution to rising EOBC incidence. Prevention strategies targeting these modifiable behaviours may have broader benefits for cancer prevention.