Table 1. Patient characteristics in studies included in the meta-analysis.
| Study reference, year | Year of publication | Country(ies) | Study design | Study Population | Sample size | Breast cancer cases (%) | Age, Mean (SD) | Blood samples | Biochemical assay | Breast cancer diagnosis | Time between measurement of IR and the diagnosis of cancer | Insulin resistance definition |
| Bruning PF et al 20 | 1992 | Netherlands | CC | Pre and postmenopausal | 664 | 33.6 | NA | NonfastingC-peptide | Radioimmunoassay | NA | NA | NA |
| Yam D et al 11 | 1996 | Israel | CC | NA | 25 | 40.0 | NA | Fasting insulin | Radioimmunoassay | Pathology | NA | NA |
| Del Giudice ME et al 21 | 1998 | Canada | CC | Premenopausal | 198 | 50.0 | 42.5 (5.1) | Fasting insulin | Radioimmunoassay | Pathology | NA | NA |
| Jernstrom H et al 22 | 1999 | USA | CC | Postmenopausal | 438 | 10.3 | 74.3 (9.5) | Fasting insulin | Radioimmunoassay | Pathology | NA | NA |
| Toniolo P et al 23 | 2000 | USA | CC | Pre and postmenopausal | 658 | 26.1 | 49.8 (8.4) | NonfastingC-peptide | Radioimmunoassay | Pathology records | Median: 57 months Range: 7–120 months | NA |
| Kaaks R et al 24 | 2002 | Sweden | CC | Pre and postmenopausal | 700 | 35.1 | 54.4 | Fasting insulin | Immunoradiometric assay | Pathology | Median: 2.2 yrsRange: 1 month-10.6 yrs | NA |
| Mink PJ et al 25 | 2002 | USA | CC | Pre and postmenopausal | 7894 | 2.4 | NA | Fasting insulin | Radioimmunoassay | Medical records and cancer registries | NA | NA |
| Keinan-Boker L et al 26 | 2003 | Netherlands | CC | Postmenopausal | 482 | 30.9 | 57.1 (5.5) | NonfastingC-peptide | Radioimmunoassay | Cancer registry | Median: 28 months Range: 14–73 months | NA |
| Lawlor DA et al 36 | 2004 | UK | CS | Pre and postmenopausal | 3837 | 3.8 | 68.9 (5.5) | Fasting insulin | ELISA assay | Medical records/database | Median: 6 yrs Range: 0.5–36 yrs | product of fasting glucose (mmol/l) and insulin (lU/ml) divided by the constant 22.5 |
| Schairer C et al 27 | 2004 | USA | CC | Postmenopausal | 344 | 53.8 | 64.2 (9.6) | NonfastingC-peptide | Radioimmunoassay | Pathology | Mean: 19 yrs | NA |
| Gonullu G et al 28 | 2005 | Turkey | CC | Postmenopausal | 40 | 50.0 | 47.7 (4.0) | Fasting insulin | Radioimmunoassay | Pathology | NA | [(fasting glucose (mmol/L) x fasting insulin(mU/mL))/22.5]. Value greater than 2.7 was considered as insulin resistance; IR% = 37.5 |
| Falk RT et al 29 | 2006 | USA | CC | Premenopausal | 357 | 47.8 | 38.6 (20-44)* | NonfastingC-peptide | Radioimmunoassay | Pathology | NA | NA |
| Verheus M et al 30 | 2006 | 8 european countries | CC | Pre and postmenopausal | 3345 | 34.1 | 54.5 | Fasting and nonfasting C-peptide | Radioimmunoassay | Cancer and pathology registries | Mean: 2.8 yrs Range: 0.1–6.3 yrs | NA |
| Eliassen AH et al 14 | 2007 | USA | CC | Pre and postmenopausal | 617 (insulin) | 33.7 | 45.0 | Fasting insulin | Radioimmunoassay | Medical records | Mean: 31 months Range: 1–87 months | NA |
| 945 (c-peptide) | 33.4 | Fasting and nonfasting C-peptide | ELISA assay | |||||||||
| Fair AM et al 12 | 2007 | China | CC | Pre and postmenopausal | 794 | 50.0 | 47.7 (7.9) | C-peptide (fasting status NA) | ELISA assay | Cancer registry | NA | NA |
| Garmendia ML et al 13 | 2007 | Chile | CC | Pre and postmenopausal | 340 | 50.0 | 55.8 (11.4) | Fasting insulin | ELISA assay | Pathology | NA | Insulin resistance was measured by HOMA = insulin/(22.5e-lnglucose) and defined as 2.5 or more |
| IR% = 55.3 | ||||||||||||
| Cust AE et al 31 | 2009 | Sweden | CC | Pre and postmenopausal | 1122 | 50.0 | NA | NonfastingC-peptide | Radioimmunoassay | Cancer registry | Median: 4.4 yrs | NA |
| Gunter MJ et al 32 | 2009 | USA | CC | Postmenopausal | 1651 | 50.9 | 63.5 | Fasting insulin | NA | Medical records and tumor registries | NA | HOMA-IR index = fasting insulin [µ IU/mL] × fasting glucose [mg/dL]/22.5 |
| Kabat GC et al 33 | 2009 | USA | CC | Postmenopausal | 5450 | 3.5 | 62.6 (6.6) | Fasting insulin | ELISA assay | Medical records and tumor registries | NA | ([fasting insulin(microIU/mL) x fasting glucose (mg/dL)]/22.5) |
| Abbasi M et al 37 | 2010 | Iran | CS | Pre and postmenopausal | 920 | 8.9 | 38.1 (12.0) | Fasting insulin | Radioimmunoassay | Pathology | NA | fasting insulin (mU/L) x fasting glucose (mg/dL)/405. HOMA-IR values of greater than 1.8 as indicative for insulin resistance |
| Capasso I et al 34 | 2011 | Italy | CC | Postmenopausal | 777 | 37.7 | 57.55 (45–75)* | Insulin (fasting status NA) | NA | NA | NA | NA |
| Sieri S et al 35 | 2012 | Italy | CC | Pre and postmenopausal | 1807 | 20.6 | NA | Fasting insulin | Chemiluminescent immunoassay | NA | NA | Not defined |
NA = not available; CS = cross-sectional; CC = case-control; * = Mean (range); HOMA-IR = Homeostatic model of assessment-insulin resistance; IR = Insulin resistance.