A cancer diagnosis can turn life upside down, but new research suggests that its consequences reach far beyond physical health.
Patients diagnosed with cancer are twice as likely to develop a mental disorder later in life compared with cancer-free individuals.
This is according to a new study involving nearly 300,000 Danish cancer patients who had no previous history of mental illness.
Our data show a substantial difference between people with cancer and those without cancer when it comes to developing mental disorders.
“Our data show a substantial difference between people with cancer and those without cancer when it comes to developing mental disorders,” says cancer researcher Christoffer Johansen, Clinical Professor at the Department of Clinical Medicine, University of Copenhagen and Rigshospitalet, and one of the researchers behind the study.
The study found that one in two patients developed a mental disorder within 25 years of their cancer diagnosis. Researchers also found a fivefold increase in the risk of developing a mental disorder leading to hospitalization or the prescription of psychotropic medication during the first year after diagnosis.
The risk then declines substantially but remains elevated among cancer patients. Even after ten years, the risk of developing a mental disorder is still 40 percent higher than in the general population.
“It is certainly thought-provoking that the risk remains so high after ten years. It is striking that this almost becomes a condition associated with being a cancer survivor,” says Christoffer Johansen.
The researchers examined 289,391 patients diagnosed with cancer between 1995 and 2015, including the types of cancer they developed and whether they later experienced mental disorders such as depression or anxiety. Patients with a prior mental disorder were excluded from the study.
The risk of being hospitalized for a mental disorder is 5.2 times higher among cancer patients than among cancer-free individuals during the first year after diagnosis. After ten years, the risk remains 20 percent higher.
At the same time, cancer patients are 5.5 times more likely to receive medication for mental disorders during the first year after diagnosis. After ten years, the risk remains 20 percent higher.
A mental disorder was recorded if a patient was either hospitalized for a psychiatric condition or prescribed medication to treat one. Denmark’s detailed national health registries provided the data used in the analysis.
The cancer cohort was compared with 1,031,057 cancer-free individuals matched for factors including age, sex, and socioeconomic status.
The study examines the statistical association between cancer diagnoses and mental disorders. In addition, the researchers designed the study to account for factors that might otherwise influence the likelihood of developing a mental disorder.
“Our study provides strong evidence of a causal relationship between a cancer diagnosis and subsequent mental disorders. This is because we only included patients with no previous psychiatric history, but also because the statistical effects we observed are very strong,” says Christoffer Johansen.
The findings also show that patients diagnosed with pancreatic cancer, brain cancer, esophageal cancer, lung cancer, or liver cancer face a higher risk of developing a mental disorder than patients diagnosed with, for example, breast cancer, prostate cancer, or melanoma.
Overall, cancer patients are 2.3 times more likely to develop a mental disorder than cancer-free individuals.
The following cancer diagnoses were associated with the highest statistical risk of subsequently developing a mental disorder. These figures reflect average risk across the entire follow-up period, which averaged 15 years:
“The cancers with the poorest prognosis are also the ones associated with the greatest risk of developing mental disorders. Cancers where the life expectancy is very short or where quality of life is expected to be severely impaired stand out clearly in relation to the development of mental illness,” says Christoffer Johansen, adding:
“In contrast, the chances of successful treatment and survival are much greater for breast cancer, prostate cancer, and melanoma. That is likely why we see a lower risk in these groups, although the risk remains significantly higher than among people without cancer.”
Looking at the types of mental disorders most commonly seen among cancer patients, anxiety disorders and depression are particularly prominent.
“Cancer is a disease that people know can be fatal. It represents a threat to life. As a result, receiving a cancer diagnosis is also a major psychological burden and may trigger reactions such as depression, anxiety, or fear of recurrence,” says Christoffer Johansen.
For Christoffer Johansen, the results call for changes in how the psychological aspects of cancer care are addressed.
“This is a problem we need to take seriously. Today, cancer care is primarily focused on physical treatment, and there is relatively little emphasis on treating both psychological symptoms and psychiatric disorders during the course of cancer treatment,” he says.
Specifically, he proposes that mental health should become a much more integrated part of cancer care.
“We could consider establishing mechanisms that address psychological aspects and include them from the beginning of treatment. Alternatively, responsibility could be shared with general practitioners through a structured plan for monitoring the mental health of cancer patients over time,” says Christoffer Johansen.
The researchers used detailed nationwide health registries to investigate the relationship between receiving a cancer diagnosis and subsequently developing a mental disorder. The cancer cohort was compared with a similar cancer-free group.
The study examines the statistical association between a new cancer diagnosis and later mental disorders.
A mental disorder was defined as either hospitalization for a psychiatric condition or being prescribed medication for a mental disorder.
The researchers could identify exactly why patients were hospitalized, including conditions such as anxiety disorders or personality disorders. They could also identify the types of medication prescribed, such as antidepressants or antipsychotics.
The researchers cannot entirely rule out that a small proportion of psychiatric medications may have been prescribed for other conditions, such as antidepressants used to treat insomnia. However, this factor has only minimal influence on the overall pattern observed.
To ensure that later mental disorders were not attributable to pre-existing psychiatric illness, the researchers only included patients who developed a mental disorder after their cancer diagnosis. Since previous mental illness is a strong predictor of future psychiatric disorders, this approach limits the generalizability of the findings.
Consequently, the researchers also conducted a series of sensitivity analyses showing that the study’s conclusions remained largely unchanged when using stricter definitions of mental disorders, excluding certain medications, focusing on specific patient subgroups, or including cancer patients with a history of mental illness.