The impact of depression on a person contracting cancer has long been suspected, without any study having definitely confirmed or rejected this theory. The links have now been investigated by Cédric Lemogne, a member of the team headed by Marie Zins (INSERM's Mixed Research Unit 1018 "Epidemiology and Population Health Research Centre", AP-HP, University of Versailles Saint-Quentin), who monitored 14,203 people between 1994 and 2009, including 1119 who developed cancer as diagnosed by a doctor. All of the absences from work for depression, certified by doctors, were recorded as well as many questionnaires measuring depressive moods. The results, which will be published in The American Journal of Epidemiology, do not indicate any significant association between a person experiencing the symptoms of depression during their lifetime and their subsequently contracting cancer.
The continuing increase in incidences of cancer in France is a subject that concerns healthcare professionals, patients and their families. Although research has not yet solved all of the enigmas of the way in which cancer works, some have occasionally attributed the advent of cancer to a painful personal history. "Received ideas often become ingrained", explains Cédric Lemogne, a psychiatrist at the Georges Pompidou European Hospital (AP-HP) who works in Professor Consoli's unit (Université Paris Descartes). He is the principal author of a new study of the links between these two conditions. "Ever since Hippocrates and the beginnings of medicine, the presence of "black bile" which gave rise to the term melancholia or melancholy, has meant that people have associated the condition with the development of malign tumours. Today, there are certain claims in circulation that depression could be a risk factor in cancer". These have been supported by several scientific studies yet, in concrete terms, none of the existing meta-analyses has ever succeeded in confirming or rejecting these hypotheses.
The Inserm researchers explored the links by conducting the most robust epidemiological study. From this point of view, it was important to have data available, from quite a large cohort, that was validated for both the advent of cancer (validated cases of cancer, specific dates of the diagnosis, data for the incidence or otherwise of mortality) and with respect to depression-causing events.
The set of medical data from the 14,203 people who participated since 1989 in the GAZEL cohort of former employees of EDF-GDF [the gas and electricity companies] was collected between 1994 and 2009. The advent of depression-causing events was measured from the participants' responses to a specific questionnaire provided every three years over a period of fifteen years and through diagnoses of depression by doctors when the employee was absent from work between 1989 and 1993.
On the basis of all these factors no significant association was found between the advent of depression and the subsequent advent of the five types of cancer monitored in this study (prostate, breast, colon, cancer associated with smoking, and cancer of the lymph glands or hæmatopoietic cancers (leukemias)). Consequently, being depressed does not expose a person to greater risk of cancer.
On the other hand, the fact of being diagnosed with cancer can cause symptoms of depression. Quite apart from the results of this study, researchers emphasize that patients need reassurance. "How many times does one hear their nearest and dearest saying 'you need to fight it, be strong to beat the cancer'. As it if were abnormal or even dangerous to feel despondent. I think that patients shouldn't worry if they feel depressed. What is important is to follow all the treatments. Against cancer on the one hand and against depression on the other hand".
Even if mental illness is not responsible for causing cancer, it is nevertheless associated with a greater risk of mortality from cancer. People suffering from clinical depression might tend to neglect their health or have difficulty being taken seriously. If this results in delayed diagnosis, these people could be at risk, all things being equal, of being treated too late for cancer. In the future, it will be just as important to redefine medical support for people suffering from mental disorders.
More information: dx.doi.org/10.1093/aje/kwt217