The incidence of suicide in patients with cancer in the United States is approximately twice that of the general US population. European studies also have observed increased suicide rates in persons with cancer. Using a Danish cancer registry, Yousaf et al14
found SMRs of 1.7 and 1.4 for suicide among men and women, respectively, as compared with those of the general Danish population. In Norway, Hem et al15
reported SMRs of 1.55 and 1.35. In Sweden, Björkenstam et al11
observed an SMR of 2.5 (men and women combined) for the period from 1965 to 1974 and 1.5 for the period from 1985 to 1994. Smaller studies from the United States and Australia have also noted that a history of cancer is associated with increased risk of death by suicide.16,23,24
Using data from the United States similar to those in the present analysis, Kendal25
documented that suicides occurred in 19 per 10,000 men with cancer and four per 10,000 women with cancer. However, because no account was taken of the person-time at risk after a cancer diagnosis, no meaningful comparison could be made to the incidence of suicide in the population as a whole or across patients with different forms of cancer.
We found that lung, stomach, and head and neck cancers were associated with the highest suicide rates. Several studies have observed that cancers at certain anatomic sites are associated with particularly increased suicide rates. However, the sites associated with the greatest risk vary depending on the report.5,7-9,11,12,14,15
The European studies have shown similarly elevated suicide rates in patients with lung cancer, but have not been unanimous in identifying high rates of suicide among those with stomach and head and neck cancers.5,14,15
Although the reasons for particular types of cancers to be associated with increased suicide rates are unknown, it is possible that patients with lung cancer may struggle with their grave prognoses. One study found a 25% prevalence of depression among patients with lung cancer,26
and other work has suggested that lower quality of life in patients with lung cancer is related to emotional distress.27
Examination of psychological reactions in newly diagnosed patients with gastric cancer showed high levels of psychological distress.28
Patients with head and neck cancers have a high prevalence of depression as well.29
Head and neck cancers could have a particularly devastating effect on quality of life through their impact on appearance and essential functions such as speech, swallowing, and breathing.30
Characteristics associated with suicide in the cancer population, such as older age and male sex, were similar to those in the general population.31
Suicide risk among patients with cancer as a group was highest in the years immediately after diagnosis, but remained increased for more than 15 years as compared with the suicide rates in the general population. This is similar to the elevation in suicide risk seen in breast cancer survivors in the SEER program, some of whom were included in this study, which lasted more than 25 years after diagnosis even after definitive treatment of their cancers.16
Interpretation of results from patients who survived 15 or more years after their cancer diagnosis was limited by small numbers of suicides associated with some cancer sites. However, in addition to lung and head and neck cancers, cancers of the nervous system, prostate, and cervix seemed to be associated with long-term increases in suicide risk. This is consistent with prior work that observed a high prevalence of depression and distress in patients with brain cancer.32
Other work demonstrated elevated suicide rates among men with prostate cancer in South Florida and suggested that depression was a significant risk factor.33
Similarly, a study in southern New England described depressive symptoms in long-term survivors of cervical cancer.34
Our findings should be interpreted in light of several limitations. First, cause of death may be subject to misclassification bias. Suicide is often difficult to distinguish from homicide or accidental injury and could potentially also be classified as an unexplained death. The literature is not conclusive as to the magnitude of such an effect,35-38
although some work has suggested that suicide codes are generally quite accurate.39
Second, we were unable to evaluate the potential confounding role of comorbid medical and psychiatric conditions, including characteristics that could bear on the incidence of cancer (such as tobacco and alcohol use) that may also be associated with an increased risk of suicide. Tobacco40,41
and alcohol use42,43
have been associated with increased suicide risk, although the strengths of these associations vary widely (ranging from relative risk of 1.4 to 4.3) depending on the study. Because tobacco and alcohol use can be common in patients with lung and head and neck cancer,44,45
this may account for some of the increased suicide rates in these groups of patients.
Third, we were unable to censor patients with cancer who died of suicide from the general US population mortality data collected by the National Center for Health Statistics. Given the vastly larger number of patients who commit suicide in the general population, the impact of suicides among patients with cancer on the suicide rate of the overall US population can be expected to be negligible. In addition, any bias introduced in this manner would likely be conservative.
Our data suggest that the psychological experience of cancer survivors deserves further attention, as urged by the Institute of Medicine,1,4
particularly because appropriate use of psychosocial interventions in patients with cancer can make a positive impact on quality of life.46
The role of lifestyle factors and comorbidity in determining suicide risk among patients with cancer invites further investigation, and future analyses may be augmented by the SEER-Medicare data set,47
which may help elucidate important relationships with comorbid medical and psychiatric illnesses.