Study	Reason for exclusion
Bostick 1993	Cohort study: Iowa Women's Health Study cohort Selenium exposure not assessed according to eligibility: only intake of selenium supplements yes/no in questionnaire assessed
Brock 1991	Case‐control study with precancerous condition (carcinoma in situ of the cervix)
Chen 1988	Case‐control study
Chen 2003	Case‐control study
Connelly‐Frost 2009	Case‐control study
Costello 2001	APPOSE (Australian Prostate Cancer Prevention Trial Using Selenium): publication describes study design, trial was not started
Criqui 1991	Population‐based prospective case‐control study: Lipid Research Clinic Prevalence and Follow‐Up study Results not reported according to inclusion criteria: differences in mean selenium levels reported
Cui 2007	Nested case‐control study Selenium exposure not assessed according to eligibility: selenium measurement conducted in tissue of benign breast disease
Davies 2002	Nested case‐control study: EPIC Norfolk study cohort Results not reported according to inclusion criteria: RR estimate per unit increase in selenium level reported
Fleshner 2003	Randomised Study of Vitamin E, Selenium, and Soy Protein Isolate in Patients with High‐Grade Prostatic Intraepithelial Neoplasia: Multicomponent Intervention
Hagmar 1992	Historical cohort study
Harris 2012	Cancer was not a study endpoint
Hartman 2002	Nested case‐control study: ATBC cohort Results not reported according to inclusion criteria: differences in mean selenium levels reported; OR reported as graph and could not be calculated from reported data
Huzarski 2006	Interventional study without control group with 1489 female participants with BRCA1 mutation who received a selenium‐containing nutritional supplement
Joniau 2007	Intervention study without control group with male participants with high‐grade intraepithelial neoplasia of the prostate who received a selenium‐containing nutritional supplement
Kellen 2008	Case‐control study
Kilander 2001	Cohort study in Uppsala/Sweden Results not reported according to inclusion criteria: RR estimate per unit increase in selenium level reported
Knekt 1988a	Nested case‐control study: Mobile Health Clinic cohort Results not reported according to inclusion criteria: differences in mean selenium levels reported
Knekt 1988b	Nested case‐control study: Mobile Health Clinic cohort Results not reported according to inclusion criteria: differences in mean selenium levels reported
Knekt 1991	Nested case‐control study: Mobile Health Clinic cohort Results not reported according to inclusion criteria: differences in mean selenium levels reported
Kok 1987b	Nested case‐control study: Zoetermeer cohort Results not reported according to inclusion criteria: differences in mean selenium levels reported
Kune 2006	Case‐control study
Kuroda 1988	Case‐control study
Lawson 2007	Cohort study on multivitamin use and risk of prostate cancer
Le Marchand 2006	Case‐control study
Li 2004b	RCT for gastric cancer prevention with multicomponent intervention (200 mg synthetic allitridum and 100 μg selenium per day)
Limburg 2005	Randomised controlled trial: primary endpoint in this two‐by‐two factorial design trial with selenomethionine 200 µg daily and/or celecoxib 200 mg twice daily was the per‐participant change (regression, stable, progression) of preexisting oesophageal dysplasia—cancer incidence and mortality were not endpoints in this study
Linxian Pilot 2000	Randomised controlled trial with selenium supplements and celecoxib in participants with oesophageal squamous dysplasia in Linxian, China Endpoint was "regression of disease", cancer was not an endpoint in this investigation
Neuhouser 2009	Cohort study (Women's Health Initiative) on multivitamin use and risk of cancer and cardiovascular disease No data for selenium and cancer risk reported
Ray 2006	Cohort study (Women's Health and Aging Studies I and II) on selenium and carotenoid serum levels and mortality No data for selenium and cancer mortality reported
Rayman 2001	PRECISE trial (Prevention of Cancer by Intervention with Selenium): trial has been stopped
Rendon	Randomised controlled trial: Vitamin E, Selenium, and Soy Protein in Preventing Cancer in Patients with High‐Grade Prostate Neoplasia: Multicomponent Intervention
Steevens 2010b	Cancer was not a study endpoint
Thompson 2009	Cohort study: Iowa Women's Health Study cohort Selenium exposure not assessed according to eligibility: only intake of selenium supplements yes/no in questionnaire assessed
Tsugane 1996	Case‐control and cross‐sectional studies
Ujiie 2002	A part of this study is a prospective cohort study in Miyagi/Japan Results not reported according to inclusion criteria: differences in mean selenium levels reported
van Noord 1992	Nested case‐control study: DOM cohort Results not reported according to inclusion criteria: differences in mean selenium levels reported
van Noord 1993	Nested case‐control study: DOM II cohort Results not reported according to inclusion criteria: RR estimate per unit increase of selenium level reported
van't Veer 1996	Case‐control study
Wallace 2009	Case‐control study
Watters 2009	Cohort study on smoking and prostate cancer risk. Selenium not reported as independent variable
Wright 2004	Cohort study: ATBC cohort Exposure to antioxidants was assessed using a self‐developed index
You 2005	Randomised controlled trial to test retardation of the progression of precancerous gastric lesions among 3400 adults in Shandong, China. Intervention: vitamin C, vitamin E, selenium, garlic preparation Multicomponent intervention
Yuan 2006	Nested case‐control study: Shanghai cohort study No data on selenium and cancer risk reported
Zeegers 2009	Cohort study on factors influencing recurrence or progression of bladder cancer: West Midlands Bladder Cancer Prognosis Programme

µ = micro

APPOSE = Australian Prostate Cancer Prevention Trial Using Selenium ATBC = alpha‐tocopherol, beta‐carotene cancer prevention study BRCA = breast cancer DOM = Diagnostic Onderzoek Mammacarcinoom EPIC = European Prospective Investigation of Cancer m = milli g = gram

OR = odds ratio PRECISE = Prevention of Cancer by Intervention with Selenium RCT = randomised controlled trial