We present a contemporary analysis of risk of suicide among over 8.6 million cancer patients and report that suicide risk varies as a function of disease site, age, gender, marital status, and time after diagnosis. The risk of suicide among cancer patients is four times that of the general population and has increased from the twofold risk reported in 20023. The relative risk of suicide, vs the general population, is highest in those with cancer of the lung, head and neck, testes, and Hodgkin lymphoma. This relative risk of suicide decreases for most patients followed more than 5 years after diagnosis; however, risk remains elevated or rises for those with Hodgkin lymphoma and testicular cancer. The plurality of suicides occurs in adults >50 years of age with cancer of the prostate, lung, colorectum, and bladder, particularly among white, unmarried males.

Most cancer patients now die of non-cancer causes9. The results of the current work suggest that suicide-prevention strategies may be aimed at those >50 years of age with cancer of the prostate, lung, colorectum, and bladder; as well as patients with leukemias, lymphomas, and germ cell tumors. We recommend that providers follow the evolving guidelines for monitoring distress and suicide prevention from the American College of Surgeons Committee on Cancer, the American Society of Clinical Oncology, the National Comprehensive Cancer Network, and Action Alliance for Suicide Prevention5,6,7.

Cancer patient risk of suicide vs general population

With respect to Objective 1, we found that although suicide contributed to 0.154% of deaths among cancer patients, the risk of suicide is 4.4 times that of the general population (Table 1, Fig. 1), which has increased from 1.9 in patients diagnosed 1973-20023. The SMR of suicide in the United States (SMRs of 9.0 for men and 4.0 for women), is higher than that in other countries. In Denmark10, SMRs are 1.7 for men and 1.4 for women. In Norway11, SMRs are 1.6 for men and 1.3 for women. Notably, SMRs may not be compared to one another (only to the reference population), and these differences among the countries may be due to different rates of suicide in the general populations. SMRs may be rising in the US because of the aging cancer population12 and because most cancer patients are diagnosed with low-risk disease that is unlikely to cause cancer-specific mortality9. Male cancer patients are at higher risk than females, similar to the general population13.

The SMRs are significantly higher among recently diagnosed patients (i.e., 2011–2014) compared to patients diagnosed before 2011 (Table 1). Patients diagnosed in more recent years have a shorter follow up time (i.e. until 2017) compared to those diagnosed in the 1970–2000s. Since the SMRs are generally highest in the first few years after diagnosis vs >5–10 years after diagnosis (per Fig. 1), the SMRs for the most recent patients are skewed and are higher than patients diagnosed in prior years. Notably, since SMRs are a measure to the standardized population (the general US population in this case), SMRs should not be compared to each other, and the SMRs from Objective 1 should not be compared to the ORs in Objective 2, described below.

Additionally, we found that SMRs are highest among those diagnosed at a younger age, consistent with previous works showing that young cancer patients are a higher risk to die of any cause9. Notably, patients with testicular cancer have an SMR of suicide that increases over the follow-up period (SMR > 17 by 5+ years), suggesting that these patients should experience elevated distress and may benefit from close monitoring and early intervention5,6. These results add to the work by Fossa et al., which demonstrated that testicular cancer patients had SMRs of 1.34 for all non-cancer causes of death14. Similarly, patients with Hodgkin lymphoma remain at an elevated risk to die of suicide through the follow up period (SMRs 15–25, higher than most other cancers). Both subsets of cancer patients may receive systemic therapy and radiation therapy that cause infertility. Our results support the work by Kjaer et al.15 who reported increased risk of suicide (hazard ratio, 1.68) among Danish women with fertility problems.

Finally, compared to the analysis that include patients up to 20023, we found that head and neck cancer patients are not the disease site at greatest risk of suicide vs the general population. This finding may be secondary to the shifting distribution of human papilloma virus-associated cancers, and a decrease in those associated with tobacco and alcohol.

Previously, Kumar et al.16 used the SEER database to compare suicide rates among cancer patients in the USA diagnosed in 2007–2013 vs those diagnosed in 2000–2006. The authors reported that (1) cancer patients are at a 1.37-fold higher risk of committing suicide vs the general population; (2) the risk is highest in older males, in the first year of diagnosis; and (3) the rate of suicide has not increased between the two time periods included (i.e. 2007–2013 vs 2000–2006).

Our current work adds to the work by Kumar et al. First, we characterize suicide rates from 1973 to 2015, and we find that the OR of suicide is decreasing in more recent years vs previous years (i.e. 2011–2014 vs 1973–1980), however the risk of suicide vs. the general population is increasing: 1.9 in patients diagnosed 1973–20023, vs. 4.4 for patients in the current work who were diagnosed 1973–2015. Additionally, we compare the relative risk of death from suicide vs the general population (in Objective 1), as well as vs other cancer patients (in Objective 2). Further, we identify distinct subgroups of cancer patients who contribute to the plurality of suicides, i.e. those >50 years of age with cancer of the prostate, lung, colorectum, and bladder; as well as patients with leukemias, lymphomas, and germ cell tumors. The results of the current study may be used to guide interventions for suicide prevention among unique subgroups.

Cancer patient risk of suicide vs other cancer patients

With respect to Objective 2, we found that the plurality of suicides occurs adults >50 years of age with cancer of the prostate, lung, colorectum, and bladder (Table 2, Fig. 2). Cancer is typically diagnosed among the elderly, and these cancers are not prevalent among younger patients; in contrast, leukemias, lymphomas, and testicular cancer are more common among younger patients, and adolescents who are subsequently diagnosis have an elevated risk of suicide.

We found that men have an OR of 5.16 in committing suicide, which corroborates in our findings from Objective 1, and is also likely secondary to the incidence of testicular cancer being only in male patients. Additionally, patients who were unmarried had 65% of the odds of committing suicide, those who were white had almost 400% as those who were black. The odds of suicide were highest among those diagnosed in more distant decades, likely because of the increase time at risk, particularly among cancer survivors.

The OR of suicide of patients diagnosed in more recent years is lower than that diagnosed in previous years (e.g. 2011–2014 vs 1973–1980 in Table 2), suggesting that patients diagnosed in more recent years are less likely to commit suicide than patients diagnosed in previous years. This finding is likely secondary to the evolving characteristics of cancer patients in the USA; with a decrease in smoking rates (highest among elderly white males), there is a decrease in rates of lung cancer and human papilloma virus (HPV)-negative head and neck cancers, which have also historically been cancers of elderly white men. In contrast, with the advent of screening mammography and prostate specific antigen (PSA) testing in the 1990s, there has been a surge in the diagnoses of low-risk breast and prostate cancers1. ORs compare the odds of suicide of the group of one group of cancer patients vs a reference group of cancer patients, unlike the SMRs in Objective 1, which compare relative risk of death vs. the entire US population, as a function of time after diagnosis. Thus, if there is a change in the rate of suicide in subpopulations of patients between two eras, this change will be reflected in the ORs, but not necessarily in the SMRs.

Our work has limitations. The overall number of deaths from suicide was relatively limited overall (<1% of cancer patients), and more detailed analyses on risk factors could not be performed. Treatment paradigms have changed since the 1970s; for example, Hodgkin lymphoma patients are now treated with limited chemotherapy, and possibly a relatively low dose of very targeted radiation17. Additionally, patients having death events in earlier years (i.e. 1973–1983) have limited follow up and less time at risk (≤10 years) than some patients with events in more recent years. This may have resulted in an overestimate of SMRs for individuals diagnosed between 2011–2014, compared to those diagnosed before 1980. Similarly, patients diagnosed in recent years have short follow-up and lower chance of death from any cause.

Further, there is a risk of bias and misclassification of suicide in the SEER18,19. For example, in a review of cases of non-Hodgkin lymphomas, agreement in the subclassification of histologies between the expert review and the SEER registry record varied from 5 to 100%20. An investigation of the California Cancer Registry, which contributes to the national SEER data21, revealed registry sensitivity of receipt of radiation therapy of only 72%. As of 2018, there has been limited research published regarding the misclassification of cause of death in the SEER database. Thus, we are unable to characterize misclassification of suicide in the current work.

Nonetheless, for suicide, there is likely little discrepancy in the cause of death, as compared to a cause of death like heart disease, which may be cause by the cancer treatment, underlying heart disease, or a combination of both. We agree with Sun and Trinh, in their assessment of the SEER database, that although there may be some errors in large registries, the errors are likely less frequent than those in hospital based databases and big data will continue to remain an integral part of hypothesis-generating exploratory analyses in medical research19.

The results of the current work suggest that suicide-prevention strategies may be aimed at those >50 years of age patients with cancer of the prostate, lung, colorectum, and bladder; as well as patients with leukemias, lymphomas, and germ cell tumors. We recommend that providers follow the evolving guidelines for monitoring distress and suicide prevention from the American College of Surgeons Committee on Cancer, the American Society of Clinical Oncology, the National Comprehensive Cancer Network, and Action Alliance for Suicide Prevention5,6,7.