Risk factors and natural history of breast cancer in younger Chinese women.

Aim: To investigate the age differences in the risk factors, clinicopathological characteristics and patterns of treatment of female breast cancer patients.
Methods: Seven thousand one hundred and fifty-two women with primary breast cancer from the Hong Kong Breast Cancer Registry were recruited after receiving patients' consent, they were asked to complete standardized questionnaires which captured their sociodemographic characteristics and risk factors associated with breast cancer development. Among them, clinicopathological data and patterns of treatment were further collected from medical records of 5523 patients with invasive breast cancers. Patients were divided into two groups according to the age at diagnosis: younger (< 40 years old) vs older patients (≥ 40 years old) for subsequent analyses.
Results: Analysis on the sociodemographic characteristics and exposure to risk factors were performed on 7152 women with primary breast cancer and the results revealed that younger patients were more likely to have unhealthy lifestyles; these include a lack of exercise (85.4% vs 73.2%, P < 0.001), having high stress in life (46.1% vs 35.5%, P < 0.001), having dairy/meat-rich diets (20.2% vs 12.9%, P < 0.001), having alcohol drinking habit (7.7% vs 5.2%, P = 0.002). Younger patients were also more likely to have hormone-related risk factors including nulliparity (43.3% vs 17.8%, P < 0.001) and an early age at menarche (20.7% vs 13.2%, P < 0.001). Analyses on clinicopathological characteristics and patterns of treatment were performed on 5523 women diagnosed with invasive breast cancer. The invasive tumours in younger patients showed more aggressive pathological features such as having a higher percentage of grade 3 histology (45.7% vs 36.5%, P < 0.001), having a higher proportion of tumours with lymphovascular invasion (39.6% vs 33.2%, P = 0.003), and having multifocal disease (15.7% vs 10.3%, P < 0.001); they received different patterns of treatment than their older counterparts.
Conclusion: Younger patients in Hong Kong are more likely to encounter risk factors associated with breast cancer development and have more aggressive tumours than their older counterparts.