Past researchers have hypothesized that high extroversion and low neuroticism are related to an increased risk of cancer. There have also been studies purporting to show these personality traits influence cancer indirectly because they are associated with behaviors that may lead to cancer. However, larger studies have found no relationship.

Pernille Hansen, lead author of the study, and a team of investigators reviewed cancer history, health behavior, and personality trait data collected from 29,595 Swedish twins enrolled in the Swedish Twin Registry. These twins were born between 1926-1958 and were followed an average 25 years.

In total, 1898 cases of cancer were reported in the sample. Statistical analyses found no association between neuroticism or extroversion and any type of cancer.

"We found no indication of an association between certain personality traits and risks for cancer," conclude the authors, "nor did we find support for an indirect association where certain personality traits influence health behavior and thus indirectly affect risk for cancer."