Dostal 2015.
| Study characteristics | ||
| Methods | RCT, parallel, double‐blind in USA ‐ Minnesota Green Tea Trial (MGTT) | |
| Participants | Participants: 1075 post‐menopausal women (538 in the treatment group and 537 in the control group) Inclusion criteria: age 50‐70 years, classified as having high mammography density attending annual screening mammogram at 8 clinical centres in the Minneapolis‐St. Paul metropolitan area (Minnesota Green Tea Trial (MGTT), planning to reside in or near Minnesota for study duration. Exclusion criteria: tested positive for serological status of hepatitis B surface antigen or antibodies to hepatitis C virus; baseline ALT > 1.5 times the upper limit of 60 U/L; any history of cancer; any history of proliferative breast disease; history of breast augmentation; BMI < 18.5 or > 40 kg/m2; weight change > 4.6 kg during the previous 12 months; current or recent (within 6 months) use of HRT; current use of anti‐inflammatory agents including methotrexate or etanercept; current smoker; regular consumption of ≥ 7 alcoholic beverages/week; and regular consumption of ≥ 1 cups of green tea/week. Full details reported in Samavat et al. 2015. Recruitment: from August 2009‐April 2013 |
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| Interventions | Treatment group: 4 oral GTE capsules, i.e. 1315 (± 116) mg of total catechins/d, including 843 (± 44) mg of EGCG Control group: placebo Duration: 1 year |
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| Outcomes | Primary outcome Effects on biomarkers of breast cancer risk: mammographic density, circulating reproductive hormones and circulating insulin‐like growth factor axis proteins Secondary outcome Circulating F2‐isoprostanes, urinary oestrogen metabolites, anthropometric variables and obesity‐associated hormone concentrations QoL Safety data |
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| Green tea in exposure categories | N/A | |
| Notes | Funding: from National Institutes of Health/National Cancer Institute grant R01 CA127236, Award Number T32CA132670 from the National Cancer Institute, the Department of Defense/US Army Medical Research and Materiel Command Award Number W81XWH‐11‐1‐0013, the University of Minnesota Agricultural Experiment Station Project Number MIN‐18‐103 and the National Center for Advancing Translational Sciences of the National Institutes of Health Award Number UL1TR000114 | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | Quote: "A detailed description of the Minnesota Green Tea Trial (MGTT) design, eligibility criteria, study conduct and patient flow through the trial will be published separately (Samavat et al., Cancer Causes and Control)." reporting that "Investigational Drug Services (IDS) pharmacy utilized a computer generated randomisation scheme using the permuted block method" Comment: probably low risk |
| Allocation concealment (selection bias) | Low risk | Quote: "A detailed description of the Minnesota Green Tea Trial (MGTT) design, eligibility criteria, study conduct and patient flow through the trial will be published separately (Samavat et al., Cancer Causes and Control)." reporting that "Randomization was performed by the Investigational Drug Services (IDS) pharmacy at University of Minnesota Medical Center ‐ Fairview". Central allocation. Comment: probably done |
| Blinding of participants and personnel (performance bias) All outcomes | Low risk | Quote: from Samavat 2015 “In this double‐blinded study, study staff, participants, laboratory personnel and all parties involved with assessment of the study endpoints were blinded to treatment assignment. The treatment codes were only available to the IDS [Investigational Drug Services] pharmacy staff in charge of randomisation and a study biostatistician.” From Dostal 2015 : “Participants, investigators, laboratory staff and those monitoring clinical outcomes and adverse events were blinded to treatment assignment” and “Placebo capsules were identical in appearance to GTE". Study investigators were kept blinded to the assigned treatment of all participants experiencing an adverse effects Comment: probably done |
| Blinding of participants and personnel (performance bias) Non‐melanoma skin cancer incidence | Low risk | Quote: from Samavat 2015 “In this double‐blinded study, study staff, participants, laboratory personnel and all parties involved with assessment of the study endpoints were blinded to treatment assignment. The treatment codes were only available to the IDS [Investigational Drug Services] pharmacy staff in charge of randomisation and a study biostatistician.” From Dostal 2015 : “Participants, investigators, laboratory staff and those monitoring clinical outcomes and adverse events were blinded to treatment assignment” and “Placebo capsules were identical in appearance to GTE". Study investigators were kept blinded to the assigned treatment of all participants experiencing an adverse effects Comment: probably done |
| Blinding of participants and personnel (performance bias) Gynaecological cancer incidence | Low risk | Quote: from Samavat 2015 “In this double‐blinded study, study staff, participants, laboratory personnel and all parties involved with assessment of the study endpoints were blinded to treatment assignment. The treatment codes were only available to the IDS pharmacy staff in charge of randomisation and a study biostatistician.” From Dostal 2015 : “Participants, investigators, laboratory staff and those monitoring clinical outcomes and adverse events were blinded to treatment assignment” and “Placebo capsules were identical in appearance to GTE". Study investigators were kept blinded to the assigned treatment of all participants experiencing an adverse effects Comment: probably done |
| Blinding of outcome assessment (detection bias) All outcomes | Low risk | From Dostal 2015 "Participants, investigators, laboratory staff and those monitoring clinical outcomes and adverse events were blinded to treatment assignment" and "Placebo capsules were identical in appearance to GTE". Study investigators were kept blinded to the assigned treatment of all participants experiencing an adverse effects Comment: probably done |
| Blinding of outcome assessment (detection bias) Non‐melanoma skin cancer incidence | Low risk | From Dostal 2015 "Participants, investigators, laboratory staff and those monitoring clinical outcomes and adverse events were blinded to treatment assignment" and "Placebo capsules were identical in appearance to GTE". Study investigators were kept blinded to the assigned treatment of all participants experiencing an adverse effects Comment: probably done |
| Blinding of outcome assessment (detection bias) Gynaecological cancer incidence | Low risk | From Dostal 2015 "Participants, investigators, laboratory staff and those monitoring clinical outcomes and adverse events were blinded to treatment assignment" and "Placebo capsules were identical in appearance to GTE". Study investigators were kept blinded to the assigned treatment of all participants experiencing an adverse effects Comment: probably done |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | Number and reason of participants' withdrawal from the study reported. Study authors performed an ITT analysis. |
| Incomplete outcome data (attrition bias) Non‐melanoma skin cancer incidence | Low risk | Number and reason of participants' withdrawal from the study reported. Study authors performed an ITT analysis. |
| Incomplete outcome data (attrition bias) Gynaecological cancer incidence | Low risk | Number and reason of participants withdrawal from the study reported. Authors performed an ITT analysis. |
| Selective reporting (reporting bias) | Low risk | Results to the Minnesota Green Tea Trial RCT (ClinicalTrials.gov identifier (NCT number): NCT00917735) reported in several publications all included in this review. |
| Other bias | Unclear risk | Elevated number of withdrawals |