To what extent are psychological variables considered in the study of risk and protective factors for suicidal thoughts and behaviours in individuals with cancer? A systematic review of 70 years of research.

Psychological variables substantially shape the risk of suicidal thoughts and behaviours (STBs). However, it is unclear to what extent they are considered in individuals with cancer. We synthesized the quantitative research landscape concerning psychological risk/protective factors of STBs in the (psycho-) oncological context. This pre-registered review (PROSPERO-ID CRD42022331484) systematically searched the databases PubMed/Medline, CINAHL, PsycInfo, Cochrane Library, and Web of Science (as well as the grey literature and preprints). Risk of bias (RoB) was estimated using the ROBINS-I tool. Of 11,159 retrieved records, 319 studies were eligible for inclusion. Of those, 163 (51.1%) had investigated psychological factors (affective: n = 155; social: n = 65; cognitive: n = 63; personality/individual differences: n = 37; life events: n = 6), in a combined 3,561,741 participants. The most common STBs were suicidal ideation (n = 107) or death wishes (n = 20) rather than behaviour (suicide deaths: n = 26; attempts: n = 14). Most studies had a serious RoB. Thus, a large body of research investigated STBs in cancer patients/survivors, but it rarely aligned with the theoretical or clinical developments in suicide research. We propose a conceptual model of STBs in cancer delineating moderation and mediation effects to advance the integration of the fields, and to inform future research and practice.