Reply to “Mental disorders and mortality in cancer survivors: Key unaddressed factors”

Thank you for the opportunity to respond to the comments of Drs Zuyin Ge and Sheng Li. We also thank them for their interest in our article¹ and for taking the time to express their concerns.

In their letter to the editor, Ge and Li noted potential concerns about the effects of the coronavirus disease 2019 (COVID-19) pandemic on mental health and mortality because of the reallocation of health care resources. The pattern of psychological disease incidence has changed substantially during the COVID-19 pandemic in South Korea, with a decrease in organic mental disorders and substance-related disorders and an increase in anxiety disorders.² However, no excess mortality was observed during the early stages of the pandemic, up to October 2021. Although excess mortality started to increase in November 2021,³ during most of the study period, the mortality rate was not affected by the COVID-19 pandemic. Considering COVID-19 as a confounder, the COVID-19 pandemic should be associated with both mental disorders and mortality. Thus, during the study period (until December 2021), confounding effects of the association between mental disorders and mortality were minimal. In addition, when we compared the cumulative incidence of mental disorders by year, the pattern of increase was consistent throughout the study period. However, we agree with their concerns and, if studies include 2022, the effects of COVID-19 should be considered.

Regarding sex differences in mental disorders, there is a higher incidence of most mental disorders in female patients with cancer than in male patients; the underlying causes of the sex difference are very important, as Ge and Li suggest. However, because the study applied claims-based data, except for health care service utilization, the available variables were limited, and the psychological challenges of individuals were not available. Therefore, we could not directly explore sex differences in mental disorders in this study. Based on the limitations of the data source, we agree that, in the future, there is a need for more studies on the mechanisms, including physiologic factors, psychological stress, and social roles, to explain sex differences in mental disorders among cancer survivors, in combination with qualitative and quantitative research methods.

Drs Ge and Li suggest that we should have examined the impact of comorbid mental disorders on mortality, considering the multiple mental disorders in cancer survivors and their increased burden. A systematic review of psychiatric comorbidities in cancer survivors identified only four of 26 articles that assessed these conditions, with the scope limited to comorbid anxiety and depression.⁴ In addition, Ter Meulen et al. considered depression and anxiety disorder comorbidities only.⁵ In our study, we divided the patients with mental disorders into five groups. However, several mental disorders were included in each group (please refer to Table S1), and the strength of the association with mortality for each mental disorder group varied (from no association to a three-fold increase in mortality). Therefore, it was difficult to define comorbid mental disorders. If several mental disorders are considered, we must consider the different strengths of the association between each disease group and mortality. If we consider the combination of mental disorders, too many groups may be created. As this makes categorizing exposure variables and interpreting the results difficult, this study focuses on each mental disorder.

The authors declared no conflicts of interest.

This work was supported by the National Research Foundation of Korea (RS-2025-00558296; RS-2023-00241942) and Korea Basic Science Institute (2023R1A6C101A009).