Risk of cancer in bipolar disorder and the potential role of lithium: international collaborative systematic review and meta-analyses.

We examined bipolar disorder (BD) as a risk factor for developing cancer and the role of lithium on cancer incidence. We conducted two systematic review and meta-analyses of population-based studies providing data on these associations. We screened articles indexed in MEDLINE, Scopus, Embase, and PsycINFO up to August 2020. The first random-effects meta-analysis, based on 4,910,661 individuals from nine studies estimated an increased risk of cancer of any kind [RR = 1.24 (1.05-1.46); p < 0.01], especially breast cancer [RR = 1.33 (1.15-1.55); p < 0.01] in BD. The second random-effects meta-analysis, based on 2,606,187 individuals from five studies did not show increased risk of cancer in people with BD using lithium, and even suggested a small protective effect both in overall [RR = 0.94 (0.72-1.22); p = 0.66] and urinary cancer [RR = 0.93 (0.75-1.14); p = 0.48] although these findings did not reach statistical significance. The current evidence highlights that cancer risk is increased in individuals with BD, particularly breast cancer in women. Lithium may have a potential protective effect on cancer, including urinary cancer. The role of lithium as a mainstay of treatment for BD is reinforced by this study.