Sample characteristics
A total of 700 cancer patients were contacted for this study. Among them, 59 eligible patients refused to join and 69 patients were not able to cooperate due to at least one of the following factors: poor physical conditions, poor mental health conditions, and low education level. Initially, 282 out of 350 eligible hospitalized patients from Zhongshan Affiliated hospital of Dalian University (response rate 80.6%), and 290 out of 350 from Second hospital of Dalian Medical University (response rate 82.9%) agreed to participate in the study, however, 28 of them failed to complete the questionnaire and dropped out in the halfway. As a result, a total of 544 patients were included in the analysis (valid rate 95.1%). The sample characteristics are displayed in Table 1. The sample consisted of both male (49.2%) and female (51.8%) patients, approximately male:female = 1:1, at average age of 59.9 years (range,19-81 years old; standard deviation, 11.6 years). The majority (78.3%) primarily lived in the cities. Over 70% of the participants were clustered into three types of cancers: digestive system cancer (29%), lung cancer (23.7%), breast cancer (18.9%). The rest were diagnosed with gynecological cancers (9.6%), brain and neck cancers (6.4%), leukemia/lymphoma (5.9%), and others (6.4%). About half of the participants had metastasis and diagnosed with cancer for more than one year. The percentage of missing data was less than 1.5% for all variables and missing data on all variables except for SI was assumed to be in the low-risk category.
Prevalence of suicidal ideation
Out of the total participants (n=544), over a quarter of them reported that they had experienced SI. The prevalence of SI was 26.3% (n=143), with 24.4% in men and 28.0% in women.
Study factors associated with suicidal ideation
The comparison of socio-demographic factors and the related clinical characteristics between the enrolled patients with and without SI is displayed in Table 2. We found no significant difference in the following demographic variables: sex, age, education attainment, or household income between the two groups (all p>0.05). A significant difference was found with marital status, employment status, metastasis, and currently diagnosed depression (all p<0.05). The comparison of the stage at diagnosis showed a marginal p value (p=0.051). In addition, the two groups of patients presented significantly different levels of health self-efficacy and profiles of physical symptoms, in particular, symptoms like pain, shortness of breath, insomnia, nausea, and lack of appetite. Based on these results, we entered socio-demographic factors, metastasis, stage at diagnosis, and depression as control variables in the subsequent analyses.
Effects of physical symptoms on suicidal ideation
Multivariate logistic regression analysis was performed to examine the effect of each physical symptoms on SI, individually. We focused on the six physical symptoms (pain, shortness of breath, insomnia, nausea, weakness, and lack of appetite) that were identified with significant or marginally significant differences in the earlier comparison between the participants with or without SI. Both insomnia (aOR=1.84, 95% CI 1.13 to 3.00, p =0.015) and lack of appetite (aOR=2.14, 95% CI 1.26 to 3.64, p =0.005) were found positively associated with SI after adjusting for socio-demographics, clinical variables, and diagnosed depression in model 3 (Table 3).
Interaction of health self-efficacy and physical symptoms on suicidal ideation
We also tested the modifying effect of health self-efficacy on the association between physical symptoms and SI. As shown in Table 4, physical symptoms of insomnia and lack of appetite were significantly associated with SI in patients with low levels of health self-efficacy. According to a difference in OR between high and low health self-efficacy, two-way interaction terms of health self-efficacy×each physical symptom were entered and tested individually. In model 3, low health self-efficacy showed a marginally significant exaggerating effect on the association between pain and SI (aOR = 2.77, 95% CI 0.99 to 7.74, p =0.053) when adjusted for all the confounding variables.
Because the depression-rating scale HDRS-17 also contains items related to the physical symptoms (i.e. sleep, weight loss, and suicide), which may confound the measures, we then performed another set of analyses by using the HDRS-12 scores that excluded the evaluation of the aforementioned physical symptoms in the depression variable. The results agreed with our previous findings, as shown in the Additional File 2 (Model 3 in Appendix Table 3 & Table 4) with the data of insomnia (aOR=1.75, 95% CI 1.07 to 2.87, p =0.026), lack of appetite (aOR=2.20, 95% CI 1.29 to 3.74, p =0.004), and low health self-efficacy × pain (aOR=2.68, 95% CI 0.96 to 7.47, p =0.056).