Abstract and Introduction
Abstract
Personality traits have been studied extensively as risk and prognostic factors for cancer; however, the association remains unclear. This prospective, population-based cohort study comprised 59,548 Swedish (1974–1999) and Finnish (1976–2004) participants who completed a questionnaire eliciting information for the Eysenck Personality Inventory and on health behavior at baseline. To analyze the association of personality traits extraversion and neuroticism with risk of cancer, the authors identified 4,631 cancer cases for a maximum 30 years of follow-up. To assess the association with cancer survival among the Finnish participants, they identified 2,733 cancer cases and, later, 1,548 deaths for a maximum 29 years of follow-up. Hazard ratios were estimated by treating the personality scales as continuous variables and are presented per one increase in score on each scale. In multivariate analyses, extraversion and neuroticism were not significantly associated with risk of cancers at all sites (extraversion: hazard ratio = 0.99, 95% confidence interval: 0.98, 1.01; neuroticism: hazard ratio = 1.00, 95% confidence interval: 0.99, 1.02). Results showed no significant association between these traits and the hazard ratio for death after cancers at all sites, and they do not support the hypothesis that extraversion and neuroticism are direct risk factors for cancer or survival after cancer.
Introduction
Personality has long been hypothesized to play a causal role in the development and progression of cancer. In 1962, Kissen and Eysenck conducted one of the first modern studies of the association between personality and cancer and reported that, compared with hospital controls, patients with lung cancer were more likely to be extraverted and less likely to be neurotic. Their theory could be interpreted to suggest that extraverts are at increased risk of cancer because they seek stimulation and thus experience high levels of stress, whereas individuals with low levels of neuroticism could be at increased risk of cancer because they tend to have a reduced emotional outlet and thus accumulate emotional stress. The higher exposure to stress could influence cancer risk by influencing immune and endocrine function. Supporting this theory, Morris et al. reported that persons with lower levels of neuroticism and trait anxiety scores were at increased risk of breast cancer.
Since then, the results of several well-conducted prospective studies have not confirmed an association between personality traits (e.g., extraversion, neuroticism, and trait anxiety) and cancer risk; however, the majority of these studies had methodological limitations, including a small number of cancer incidents (ranging from 113 (6) to 1,898 (8)), which has not provided sufficient statistical power to analyze individual cancer sites. Because combined analyses across cancer sites may produce diluted effects, site-specific analyses are needed. With a stress interpretation of the personality theory, we would expect an increased risk of, especially, immune- and endocrine-related cancers, but there has also been a layman expectation of an overall relation between personality and cancer.
Personality has also been suggested to play a role in cancer progression. Temoshok et al. observed that tumor thickness in patients with malignant melanoma was positively associated with "type C" personality, which they described as cooperative, unassertive, patient, suppressive of negative emotions, and accepting/compliant with external authorities. Persons with low levels of extraversion and high levels of neuroticism are thought to repress their emotions, which is considered to be one of the most important aspects of type C personality. The hypothesis related to cancer survival could also be interpreted as being related to stress. Accumulated repression of emotions may cause stress, which could influence cancer progression by influencing immune and endocrine function.
The role of personality traits in survival after cancer has been addressed in 8 known prospective studies, but no conclusion has been reached, and the evidence is still limited. Three studies found statistically significant associations between low extraversion levels and shorter breast cancer survival, between high scores on the lie scale (indicating rigid adherence to social norms, which has been suggested to be a characteristic of the cancer-prone personality) and non-Hodgkin lymphoma, and between high levels of neuroticism and all cancer sites combined for women. Still, 5 studies found no association between personality and cancer survival. These studies had several limitations, however, including small samples. Five of them had fewer than 200 participants and lacked sufficient statistical power to analyze individual cancer sites.
We conducted a population-based, prospective cohort study to examine the associations between personality traits and cancer risk and survival. On the basis of previous studies, we expected that a number of factors may play a role in the causal pathway between personality traits and cancer risk and survival. In particular, we expected that a number of lifestyle factors (e.g., smoking and alcohol consumption) may function as mediators and thus that the effect of personality traits works through these factors and not independently. To the best of our knowledge, ours is the largest study of the association between personality traits and cancer risk and survival.