Table 1.

Characteristics of Eligible Studies - Quantitative

First Author	Year and Country	Objectives	Phase	Study Design, Sample Size	Cancer Type	Loneliness Defined?	Loneliness Measure	Results
Pivodic et al. 21	2021 Belgium	Examine changes in physical, psychological and social well-being in the last 5 years of life of older people with cancer.	End of life	Prospective cohort N=107	Breast, prostate, lung, GI	No	Loneliness Scale of De Jong-Gierveld	Despite declines in physical function and increases in death and depressive symptoms over time, loneliness levels did not change close to death.
Rentscher et al. 20	2021 United States	Examine changes in loneliness and mental health during the COVID-19 pandemic from the Thinking and Living With Cancer (TLC) study.	Treatment	Prospective cohort N=427	Breast	Yes	Single item “I felt lonely during the past week” from the Center for Epidemiologic Studies–Depression (CES-D) Scale.	Across survivors and matched controls without cancer, loneliness did not change from study enrollment to the last pre–COVID-19 assessment, but significantly increased from the last pre–COVID-19 assessment to the COVID-19 survey, controlling for living circumstances and social support. Across survivors and controls, changes in loneliness were associated with changes in depression and anxiety symptoms. Increases in loneliness were also associated with higher perceived stress.
Ashi et al. 18	2020 Japan	Explore factors affecting social isolation and loneliness at the time of diagnosis among patients with lung cancer in Japan.	Diagnosis, Treatment	Cross-sectional N=264	Lung	No	Japanese version of the UCLA Loneliness Scale	Loneliness ranged from 16% to 41%. Univariate analysis: more patients with a history of smoking, receiving welfare (beta coefficient=0.48, 95% CI=0.13-0.83), and presenting with symptoms of dementia (beta coefficient=0.29, 95% CI=0.04-0.53). Patients who were receiving welfare (beta coefficient=0.52, 95% CI=0.13-0.90) and had dementia symptoms (beta coefficient=0.28, 95% CI=0.03-0.54) were more likely to report loneliness.
de Boer et al. 34	2020 The Netherlands	Assess prevalence of psychosocial problems and longitudinal changes in functional status, psychosocial functioning, and quality of life.	All phases	Prospective cohort N=80	Breast	No	Loneliness Scale of De Jong-Gierveld	36% of patients experienced loneliness, with 28% moderate and 8% severe. A non-clinically relevant increase in loneliness was observed between baseline (mean : 2.6 (SD3.1)) and six months (32.1 (3)) in multivariate analysis (adjusted model; b 0.7, 95% CI 0.1–1.2, p = .018).
Mathew et al. 27	2020 New Zealand	Study barriers and enablers to starting a relationship for patients with prostate cancer and characteristics of patients who were and were not in a relationship.	Not reported	Prospective cohort N=35	Prostate	No	Revised UCLA Loneliness Scale	Patients with prostate cancer in a relationship had lower levels of loneliness and better perception of emotional support.
Hyland et al. 29	2019 United States	Investigate the relationship between loneliness, depressive symptoms, quality of life, and social cognitive variables (stigma, social constraint, and cancer-related negative social expectations); Explore loneliness as a mediator between social cognitive variables and depressive symptoms/quality of life in lung cancer.	Treatment	Cross-sectional N=105	Lung	Yes	20-item UCLA Loneliness Scale-Version 3 (UCLA-V3)	Participants reported a low to moderate level of loneliness. Greater loneliness was associated with greater depressive symptoms and worse QOL. Greater stigma, social constraint, and cancer-related negative social expectations were significantly correlated with loneliness. Loneliness partially mediated the relationship of social cognitive variables with depressive symptoms and QOL.
Baitar et al. 35	2018 Belgium and the Netherlands	Determine if baseline coping strategies predict changes in psychological and physical well-being, comparing older versus middle aged patients with cancer versus older patients without cancer; Compare baseline coping strategies and well-being in each patient group.	Treatment	Prospective cohort N=263	Breast, prostate, lung, GI	No	Loneliness Scale of De Jong-Gierveld	30% impaired loneliness in older adults with cancer at baseline. At one year: Active tackling OR= 1.19 (0.56–2.51); Social support OR= 0.55 (0.25–1.19); Avoidance OR= 1.00 (0.43–2.32); Palliative reacting OR= 1.31 (0.70–2.48)
Nelson et al. 24	2018 United States	To test the feasibility, tolerability, and acceptability of CARE by examining the rates of eligibility, acceptance, and adherence	After Treatment	Feasibility study N=59	Breast, Prostate, Lung, Hematological cancer	No	UCLA Loneliness Scale-Short Form	Non-significant reduction in loneliness following use of the intervention. CARE had small effects for reduced loneliness (d=0.19 [CI: −0.34 to 0.72]) at 2 months of assessment.
Deckx et al. 33	2015 Belgium and the Netherlands	Describe social and emotional loneliness in older patients with cancer compared to younger patients and older patients without cancer; Evaluate relationship of loneliness to changes in common cancer- and ageing-related problems.	Treatment	Prospective cohort N=96	Breast, colorectal	Yes	Loneliness Scale of De Jong-Gierveld	22% of older adults felt lonely, and 35% one year later. There were no differences in perceived loneliness (younger versus older patients with cancer). Increase in loneliness was attributed to increase in emotional loneliness.
Olson Scott et al. 22	2014 United States	Explore issues of relationship with God, symptom distress and feelings of anger and loneliness in people with advanced cancer near the end of life.	End of life	Retrospective secondary analysis of RCT trial data N=354	Not reported	No	Revised Memorial Symptom Assessment Scale	Loneliness (8.2) mean scores were relatively high, meaning that these patients reported relatively little loneliness. Weak but significant relationship between loneliness and good relationship with God. Loneliness and symptom distress was negatively correlated.
Nausheen et al. 25	2010 United Kingdom	Investigate association of serum levels of proangiogenic cytokines with different indices of social support and loneliness.	Treatment	Prospective cohort N=51	Colorectum or colon or rectum	Yes	UCLA Loneliness Scale, Implicit Association Test-Loneliness	Vascular endothelial growth factor (VEGF) is an angiogenic mechanism through which loneliness may lead to worse cancer-related outcomes. High levels of implicit loneliness was an independent predictor of VEGF immune-expression.