Purpose:
Psychosocial stress, including bereavement and work-related stress, is associated with the risk of breast cancer. However, it is unknown whether it may also be linked with increased risk of benign breast disease (BBD).

Methods:
Our study leveraged 61,907 women aged 17-55 years-old from the Project ELEFANT study. BBD was diagnosed by clinician. Self-reported data on psychosocial stress over a ten-year period was retrospectively collected from questionnaires and categorised by cause (work, social and economic) and severity (none, low, and high). Odd ratios (ORs) for the development of BBD were estimated using logistic regression. The model was adjusted for age, BMI, TSH levels, smoking, alcohol consumption, family history, age of menarche, oral contraceptive usage, education and occupation.

Results:
Within our study, 8% (4,914) of participants were diagnosed with BBD. Work-related stress (OR = 1.57, 95% confidence interval [CI] = 1.46 - 1.69) and financial stress (OR = 1.34, 95% CI = 1.24 - 1.44) were significantly associated with BBD incidence, with a smaller but still significant association with social stress (OR = 1.11, 95% CI = 1.01 - 1.21). The associations remained significant after exclusion of participants with first- and second-degree family history of breast disease. The presence of multiple forms of stress did not synergistically increase risk. The neutrophil lymphocyte ratio (NLR), a marker of systemic inflammation and prognostic marker for breast cancer, was not associated with BBD.

Conclusions:
Psychosocial stress, particularly work-related and financial stress, is associated with increased risk of benign breast disease among young Chinese women.