Personality factors and breast cancer development: a prospective longitudinal study.

BACKGROUND It has been estimated that approximately 25% of all breast cancers in women can be explained by currently recognized somatic (i.e., hereditary and physiologic) risk factors. It has also been hypothesized that psychological factors may play a role in the development of breast cancer. PURPOSE We investigated the extent to which personality factors, in addition to somatic risk factors, may be associated with the development of primary breast cancer. METHODS We employed a prospective, longitudinal study design. From 1989 through 1990, a personality questionnaire was sent to all female residents of the Dutch city of Nijmegen who were 43 years of age or older. This questionnaire was sent as part of an invitation to participate in a population-based breast cancer screening program. Women who developed breast cancer among those who returned completed questionnaires were compared with women without such a diagnosis in regard to somatic risk factors and personality traits, including anxiety, anger, depression, rationality, anti-emotionality (i.e., an absence of emotional behavior or a lack of trust in one's own feelings), understanding, optimism, social support, and the expression and control of emotions. Conditional logistic regression analysis was used to identify variables that could best explain group membership (i.e., belonging to the case [breast cancer] or the control [without disease] group). RESULTS Personality questionnaires were sent to 28 940 women, and 9705 (34%) were returned in such a way that they could be used for statistical analyses. Among the 9705 women who returned useable questionnaires, 131 were diagnosed with breast cancer during the period from 1989 through 1994. Seven hundred seventy-one age-matched control subjects (up to six per case patient) were selected for the analyses. Three variables were found to be statistically significantly associated with an increased risk of breast cancer: 1) having a first-degree family member with breast cancer (versus not having an affected first-degree relative, odds ratio [OR] = 4.05; 95% confidence interval [CI] = 1.76-9.31); 2) nulliparity (i.e., having no children) (versus having had a child before the age of 30 years, OR = 2.67; 95% CI = 1.26-5.68); and 3) a relatively high score on the personality scale of anti-emotionality (versus a low score, OR = 1.19; 95% CI = 1.05-1.35). CONCLUSIONS AND IMPLICATIONS With the exception of a weak association between a high score on the anti-emotionality scale and the development of breast cancer, no support was found for the hypothesis that personality traits can differentiate between groups of women with and without breast cancer. We recommend that this study be continued and that other studies be encouraged to explore possible relationships between personality factors and the risk of breast cancer.