Prevalence of Depression in Adults With Cancer
Background: Depression has substantial effects on cancer patients' quality of life. Estimates of its prevalence vary widely. We aimed to systematically review published studies to obtain the best estimate of the prevalence of depression in clinically meaningful subgroups of cancer patients.
Design: Systematic review that addressed the limitations of previous reviews by (i) including only studies that used diagnostic interviews; (ii) including only studies that met basic quality criteria (random or consecutive sampling, ≥70% response rate, clear definition of depression caseness, sample size ≥100); (iii) grouping studies into clinically meaningful subgroups; (iv) describing the effect on prevalence estimates of different methods of diagnosing depression.
Results: Of 66 relevant studies, only 15 (23%) met quality criteria. The estimated prevalence of depression in the defined subgroups was as follows: 5% to 16% in outpatients, 4% to 14% in inpatients, 4% to 11% in mixed outpatient and inpatient samples and 7% to 49% in palliative care. Studies which used expert interviewers (psychiatrists or clinical psychologists) reported lower prevalence estimates.
Conclusions: Of the large number of relevant studies, few met our inclusion criteria, and prevalence estimates are consequently imprecise. We propose that future studies should be designed to meet basic quality criteria and employ expert interviewers.
Depression is a major public health problem and has an especially large effect on health when comorbid with a chronic medical condition. Clinicians working in cancer services have recognised that depression is often undiagnosed and untreated and that these shortcomings in care can have substantial effects, not only on patients' quality of life but also on their acceptance of cancer treatments. Important advances have been made: screening systems can help to identify depressed patients; oncologists have better ways to discuss psychological problems with their patients through advanced communication skills training and there are also new evidence-based interventions designed specifically for depressed patients attending cancer services. However, in order to plan the implementation of these advances, oncology teams need to know how many of their patients are likely to have depression.
At first glance, this information appears easy to come by. The briefest of electronic searches reveals that there are hundreds of articles that might be relevant, reflecting the importance of and interest in the topic. A number of reviews, including systematic reviews and meta-analyses have also been published. However, a closer inspection of these reviews reveals that, despite the wealth of research publications summarised, the prevalence of depression in clinically meaningful subgroups of people with cancer remains unclear with widely varying estimates that are difficult to apply clinically. This is because the published reviews have been limited by one or more of the following problems. The first problem is the inclusion of studies that have not used diagnostic interviews to assess whether participants were depressed. The most commonly used diagnostic criteria in psychiatry are those of the Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Diseases (ICD). These diagnostic criteria describe the nature, severity and duration of symptoms required to make an interview-based diagnosis of depression. Although rating scales can be used to identify patients who require further assessment (e.g. as a first stage in screening), or to monitor the course of diagnosed depression, they cannot be used to diagnose depression. The second problem is the inclusion of studies of varying methodological quality. Lack of attention to study quality is a common problem in reviews of observational studies and is important because the results of low-quality studies are likely to be biased and therefore to provide misleading estimates. The third problem concerns the pooling of data from heterogeneous samples into one overall estimate of depression prevalence for all cancer patients. This strategy makes the questionable assumptions that the prevalence is the same in different patient subgroups and that a pooled estimate is clinically meaningful. The final problem is a failure to consider the effect of different methods of diagnosing depression on prevalence estimates. Diagnostic criteria can be applied using different interview schedules administered by people with a range of expertise. In addition, the most commonly used diagnostic criteria include a number of physical symptoms which may also arise from having cancer or cancer treatments. Researchers may decide to apply these criteria without any assessment of the cause of patients' physical symptoms (the 'inclusive approach'), to exclude symptoms they judge to be cancer-related or to use alternative criteria without physical symptoms.
Although previous reviews have tried to address one or more of these problems, none has addressed all of them. We, therefore, aimed to answer the question, 'How common is depression in people with cancer?' by conducting a systematic review of relevant published studies in a way that addressed all the aforementioned problems by (i) including only studies that used diagnostic interviews to determine depression caseness; (ii) including only studies that met basic quality criteria; (iii) grouping studies into clinically meaningful subgroups of people with cancer; (iv) describing the effect on prevalence estimates of different methods of diagnosing depression.
Abstract and Introduction
Abstract
Background: Depression has substantial effects on cancer patients' quality of life. Estimates of its prevalence vary widely. We aimed to systematically review published studies to obtain the best estimate of the prevalence of depression in clinically meaningful subgroups of cancer patients.
Design: Systematic review that addressed the limitations of previous reviews by (i) including only studies that used diagnostic interviews; (ii) including only studies that met basic quality criteria (random or consecutive sampling, ≥70% response rate, clear definition of depression caseness, sample size ≥100); (iii) grouping studies into clinically meaningful subgroups; (iv) describing the effect on prevalence estimates of different methods of diagnosing depression.
Results: Of 66 relevant studies, only 15 (23%) met quality criteria. The estimated prevalence of depression in the defined subgroups was as follows: 5% to 16% in outpatients, 4% to 14% in inpatients, 4% to 11% in mixed outpatient and inpatient samples and 7% to 49% in palliative care. Studies which used expert interviewers (psychiatrists or clinical psychologists) reported lower prevalence estimates.
Conclusions: Of the large number of relevant studies, few met our inclusion criteria, and prevalence estimates are consequently imprecise. We propose that future studies should be designed to meet basic quality criteria and employ expert interviewers.
Introduction
Depression is a major public health problem and has an especially large effect on health when comorbid with a chronic medical condition. Clinicians working in cancer services have recognised that depression is often undiagnosed and untreated and that these shortcomings in care can have substantial effects, not only on patients' quality of life but also on their acceptance of cancer treatments. Important advances have been made: screening systems can help to identify depressed patients; oncologists have better ways to discuss psychological problems with their patients through advanced communication skills training and there are also new evidence-based interventions designed specifically for depressed patients attending cancer services. However, in order to plan the implementation of these advances, oncology teams need to know how many of their patients are likely to have depression.
At first glance, this information appears easy to come by. The briefest of electronic searches reveals that there are hundreds of articles that might be relevant, reflecting the importance of and interest in the topic. A number of reviews, including systematic reviews and meta-analyses have also been published. However, a closer inspection of these reviews reveals that, despite the wealth of research publications summarised, the prevalence of depression in clinically meaningful subgroups of people with cancer remains unclear with widely varying estimates that are difficult to apply clinically. This is because the published reviews have been limited by one or more of the following problems. The first problem is the inclusion of studies that have not used diagnostic interviews to assess whether participants were depressed. The most commonly used diagnostic criteria in psychiatry are those of the Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Diseases (ICD). These diagnostic criteria describe the nature, severity and duration of symptoms required to make an interview-based diagnosis of depression. Although rating scales can be used to identify patients who require further assessment (e.g. as a first stage in screening), or to monitor the course of diagnosed depression, they cannot be used to diagnose depression. The second problem is the inclusion of studies of varying methodological quality. Lack of attention to study quality is a common problem in reviews of observational studies and is important because the results of low-quality studies are likely to be biased and therefore to provide misleading estimates. The third problem concerns the pooling of data from heterogeneous samples into one overall estimate of depression prevalence for all cancer patients. This strategy makes the questionable assumptions that the prevalence is the same in different patient subgroups and that a pooled estimate is clinically meaningful. The final problem is a failure to consider the effect of different methods of diagnosing depression on prevalence estimates. Diagnostic criteria can be applied using different interview schedules administered by people with a range of expertise. In addition, the most commonly used diagnostic criteria include a number of physical symptoms which may also arise from having cancer or cancer treatments. Researchers may decide to apply these criteria without any assessment of the cause of patients' physical symptoms (the 'inclusive approach'), to exclude symptoms they judge to be cancer-related or to use alternative criteria without physical symptoms.
Although previous reviews have tried to address one or more of these problems, none has addressed all of them. We, therefore, aimed to answer the question, 'How common is depression in people with cancer?' by conducting a systematic review of relevant published studies in a way that addressed all the aforementioned problems by (i) including only studies that used diagnostic interviews to determine depression caseness; (ii) including only studies that met basic quality criteria; (iii) grouping studies into clinically meaningful subgroups of people with cancer; (iv) describing the effect on prevalence estimates of different methods of diagnosing depression.
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