The worldwide incidence of breast cancer in young patients shows an obvious upward trend in recent years. Based on the data of Surveillance, Epidemiology, and End Results, approximately 11% of breast cancer patients are 35 to 45 years old. The Asian population has a significantly higher proportion of young patients with breast cancer than the Western population, and 9.5% to 12% of all patients with breast cancer in Asia are within this young age range. Recently, the rate of breast cancer diagnosis has rapidly increased in young women in China, and the mortality rate among these young patients is higher than among those who are older. Statistics released by the International Agency for Research on Cancer have shown that patients younger than 40 years accounted for 12.56% of all cancer diagnoses in China in 2008. According to statistics of the Shanghai Center for Disease Control and Prevention, patients <40 years old accounted for 10% to 20% of the total cases of breast cancer in Shanghai from 1990 to 2007. The poor prognosis of early onset breast cancer has gradually attracted widespread international concern in recent years.[3,5]
Some countries with a high incidence of breast cancer have made significant progress identifying risk factors for breast cancer that are specific to certain regions and certain populations, which allows doctors to collect relevant information to quantitatively predict the risk of breast cancer for an individual woman. Case–control studies from different regions of China have shown that the risk factors for breast cancer are mainly biological (age at menarche, duration of breast-feeding, menopausal status, and history of contraceptive drug use), psychological (mental stress, depression, negative life events, and long-term depression), and social (passive smoking and residential environmental pollution) factors. Yan et al conducted a meta-analysis of nearly 10 years of Chinese literature to elucidate the relationship between psychological factors and breast cancer and showed that the development of breast cancer is the consequence of the integrated effect of multiple factors including biological, psychological, and social factors. Currently, research on risk factors for early onset breast cancer in China is lacking. Given the gradual increase in the incidence of early onset breast cancer, research investigating the lifestyle and status of young patients prior to disease onset is being performed to identify factors associated with early onset breast cancer. This study aimed to investigate the main physiological and psychological risk factors for breast cancer in young patients based on the biopsychosocial medical model and to explore the impact of lifestyle and psychological stress on the development of early onset breast cancer, thereby providing a basis for the development of relevant prevention strategies.