Personality Does Not Influence Cancer; Hypothesis Should Be Retired

Zosia Chustecka

August 27, 2010

August 27, 2010 — Personality has no effect on cancer risk or cancer survival, concludes a new study based on the largest and most relevant dataset to date. Other recent studies have also found no link or have been inconclusive.

It is time to finally retire the hypothesis that personality has an effect on cancer, say psychologists reporting and discussing these findings in the August 15 issue of the American Journal of Epidemiology.

In the study, Naoki Nakaya, PhD, and colleagues from the Institute of Cancer Epidemiology at the Danish Cancer Society in Copenhagen, analyzed data from more than 4500 cancer patients and found no effect of personality on either risk or survival.

"Cancer patients should not think that their personality traits may have affected their cancer or cancer prognosis," the researchers conclude.

Given the evidence, we think that it is time to retire the hypothesis.

"Given the evidence, we think it is time to retire the hypothesis that personality — as it has been studied until now — is causally related to the onset of and survival from cancer," said Adelita Ranchor, PhD, professor of health psychology at the University of Groningen, the Netherlands.

"Studies so far have failed to find any epidemiological evidence," she told Medscape Medical News.

Dr. Ranchor coauthored an editorial that accompanied the study with Robbert Sanderman, PhD, also from the University of Groningen, and James C. Coyne, PhD, professor of psychiatry at the University of Pennsylvania in Philadelphia.

Dr. Nakaya, principal investigator of the study, told Medscape Medical News that he agrees that it is time to retire this hypothesis, and urges physicians to tell cancer patients about these findings so that they can stop worrying.

"Many patients worry that their own personality has made their cancer develop, or that their personality shortens longevity," Dr. Nakaya said. "But our research shows that this is not the case, so cancer patients need not worry about this," he reported.

"The notion that personality is related to cancer onset and its course might cause turmoil for the patients and their families because there might be some pressure on the patient to fight the cancer," Dr. Ranchor added. If doctors see that the patient and family are struggling with this issue, then providing relevant information can bring some peace of mind, she explained.

Strongly Held Cultural Beliefs

The hypothesis that personality influences cancer can be traced back to the times of the Ancient Greeks, the editorialists note. The idea resurfaced in the 1960s after a few positive studies — which have since been severely criticized — led to the idea that some personality traits lead to an increased risk for cancer, and that once cancer has developed, optimism and a fighting spirit can extend survival.

Some of these ideas have now become "embedded in a matrix of strongly held cultural beliefs," the editorialists note.

Many of the theories on personality and cancer were proposed by Hans Eysenck, who was involved in some of the early studies and who developed the personality test that was used to measure extraversion and neuroticism in many of these studies.

The personality test itself is "well validated and widely accepted," the editorialists point out, "but Eysenck's views on the relation of personality to cancer are not."

He was "one of the most vigorous proponents of personality as a risk factor for cancer," and even though much of his work in this field has since been discredited, his ideas are still influential because not everyone is aware of the criticisms surrounding his controversial work, which continues to be cited, Dr. Ranchor said.

On the basis of a small study, published in 1962, that found that lung cancer patients were more likely than control subjects to score high on extraversion and low on neuroticism, Eysenck proposed that these personality traits affect an individuals' risk for cancer because they affect stress, which in turn affects the immune and endocrine systems. His explanation for this was that people who scored high for extraversion would seek out stimulation and would therefore experience high levels of stress, and that people who scored low for neuroticism (which measures emotional instability) would tend not to express their feelings and would therefore experience a high level of emotional stress.

Some of these theories were extended to cancer patients, with the idea that the accumulated repression of emotions would cause stress, which again, through an effect on immune and endocrine functions, would have a negative effect on cancer progression.

This led to the idea that psychological factors such as optimism and fighting spirit can have a positive effect on cancer. "These views are still widely held, even though evidence from high-quality studies does not support these theories, and no reasonable mechanisms to explain how the effect can be mediated have been identified," Dr. Ranchor explained.

Although the idea that a fighting spirit prolongs survival offers a sense of hope, it can also cause turmoil in the lives of cancer patients and their families, which is very sad when patients have only a limited time left, Dr. Ranchor said. Patients might be accepting of the disease, but the family thinks that they should fight because they want the patient to recover. And of course, patients themselves can become seriously disappointed if they think it is possible to fight the disease when it "turns out that it is not," she added.

If the doctor sees that the patient and/or family are struggling with such issues, providing relevant information might help, she said.

Latest Study Largest So Far

This study by Dr. Nakaya and colleagues — which is "undoubtedly the largest relevant dataset ever assembled" — found no association between personality traits and all-cancer incidence or mortality, the editorialists write. These null results should be given a weight that takes into account not only the study's superior sample size but also its methodological strengths, they explain.

We can now be reasonably confident.

"We can now be reasonably confident that the overall effect size for a personality–cancer causal association is much too small to have clinical and public health implications, if it exists at all," the editorialists write.

The hypothesis that personality can influence cancer should "quietly pass into oblivion," they suggest. However, they acknowledge that it is not likely to disappear because of "strongly held cultural beliefs and ideology."

Conducted in Scandinavia

The study was conducted while Dr. Nakaya was at the Danish Cancer Institute — he has since returned to Japan, and is now at the Kamakura Women's University. The team was headed by Christoffer Johansen, MD, PhD, DMSc, head of the department of psychosocial cancer research at the Institute of Cancer Epidemiology at the Danish Cancer Society.

They analyzed data collected in twin studies conducted in Sweden and Finland, in which all participants completed personality questionnaires, and linked it to data collected in the national cancer registries of both countries.

For the analysis of the association with risk for cancer, data from both Sweden and Finland were used. It involved 59,548 individuals who had completed questionnaires and 4631 cases of cancer, with a maximum of 30 years follow-up.

For the analysis of the association with cancer survival, only data from Finland were used. It involved 2733 cancer cases and 1548 subsequent deaths, with a maximum of 29 years of follow-up.

Neither analysis found any association between extraversion or neuroticism and the risk for cancer at any site or the risk for death from cancer at any site.

"Our findings are in line with those of recent prospective studies, which provide no support for the hypothesis that personality traits are direct risk factors for cancer at all sites," the researchers conclude.

They note, however, that their own study found a significant positive but very weak association between extraversion and neuroticism and the risk for lung cancer; this has also been seen in previous studies. They explain this by suggesting that this effect is mediated through smoking — people with a certain personality are more likely to smoke, increasing their risk for lung cancer.

The team also found a significant negative association between neuroticism and the risk for liver cancer, but they suggest that this might be a chance finding. There was no mediation by alcohol consumption, and the numbers were small, they add.

The editorialists discuss both of these findings, and agree that smoking might explain the increased risk for lung cancer, but "no plausible biological pathway can be mustered" to explain the reduced risk for liver cancer. "We might concede that both are due to chance, rather than embrace one finding but not the other," they add.

Am J Epidemiol. 2010;172:377-385, 386-388. Abstract, Abstract

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