Table 1. Characteristics of included studies on the relationship between active or passive smoking and breast cancer.
| Reference | Authors | Year of publication | Region of China | Study design | Number of cases | Number of controls | NOSa | Includedb |
| [16] | Lu et al. | 1992 | Shanghai | Case-control | 552 | 552 | B | 2 |
| [17] | Liu et al. | 1994 | Guangdong | Case-control | 125 | 250 | B | 3 |
| [18] | Ye et al. | 1995 | Anhui | Case-control | 100 | 100 | B | 3 |
| [19] | Lai et al. | 1996 | Taiwan | Case-control | 114 | 228 | B | 1 |
| [20] | Xu et al. | 1997 | Hebei | Case-control | 101 | 101 | B | 1 |
| [21] | Yang et al | 1997 | Taiwan | Case-control | 244 | 450 | B | 1 |
| [22] | Liu et al. | 1998 | Chongqing | Case-control | 155 | 155 | B | 3 |
| [23] | Tan et al. | 1998 | Hunan | Case-control | 146 | 146 | B | 3 |
| [24] | Wei et al. | 1998 | Heilongjiang | Case-control | 160 | 320 | B | 1 |
| [25] | Huang et al. | 1999 | Taiwan | Case-control | 150 | 150 | A | 1 |
| [26] | Zhao et al. | 1999 | Sichuan | Case-control | 265 | 265 | B | 2 |
| [27] | Liu et al. | 2000 | Chongqing | Case-control | 186 | 186 | B | 3 |
| [28] | Zhu et al. | 2000 | Jiangsu | Case-control | 116 | 116 | B | 3 |
| [29] | Cao et al. | 2001 | Guangdong | Case-control | 348 | 348 | B | 3 |
| [30] | Lin et al. | 2001 | Shandong | Case-control | 186 | 186 | B | 3 |
| [31] | Zha et al. | 2001 | Guangdong | Case-control | 352 | 352 | B | 3 |
| [32] | Zou et al. | 2002 | Hubei | Case-control | 112 | 112 | B | 2 |
| [33] | Shrubsole et al. | 2004 | Shanghai | Case-control | 1,459 | 1,556 | A | 3 |
| [34] | Louis et al. | 2005 | Hongkong | Case-control | 198 | 358 | B | 1 |
| [35] | Shannon et al. | 2005 | Shanghai | Cohort | 378 | 1,070 | A | 3 |
| [36] | Chou et al. | 2006 | Taiwan | Case-control | 146 | 285 | B | 1 |
| [37] | Huang et al. | 2006 | Guangdong | Case-control | 133 | 133 | B | 2 |
| [38] | Li et al. | 2006 | Sichuan | Case-control | 104 | 154 | B | 1 |
| [39] | Li et al. | 2006 | Sichuan | Case-control | 121 | 211 | B | 1 |
| [40] | Li et al. | 2006 | Liaoning | Case-control | 449 | 363 | B | 1 |
| [41] | Wang et al. | 2006 | Zhejiang | Case-control | 101 | 101 | B | 3 |
| [42] | Wang et al. | 2006 | Zhejiang | Cohort | 84 | 269 | A | 2 |
| [43] | Jin et al. | 2007 | Jiangsu | Case-control | 206 | 214 | B | 2 |
| [44] | Li et al. | 2007 | Hebei | Case-control | 175 | 175 | B | 3 |
| [45] | Ma et al. | 2007 | Shandong | Case-control | 105 | 100 | B | 1 |
| [46] | Lin et al. | 2008 | Zhejiang | Case-control | 237 | 237 | B | 3 |
| [47] | Ren et al. | 2008 | Liaoning | Case-control | 200 | 200 | B | 3 |
| [48] | Nie et al. | 2009 | Yunnan | Case-control | 200 | 200 | B | 1 |
| [49] | Wang et al. | 2009 | Chongqing | Case-control | 367 | 367 | B | 1 |
| [50] | Zhang et al. | 2009 | Guangdong | Case-control | 438 | 438 | B | 2 |
| [51] | Zhang et al. | 2009 | Zhejiang | Case-control | 1,009 | 1,009 | B | 3 |
| [52] | Qian et al. | 2010 | Jiangsu | Case-control | 698 | 813 | B | 1 |
| [53] | Shi et al. | 2010 | Jiangsu | Case-control | 223 | 223 | B | 3 |
| [54] | Shrubsole et al. | 2011 | Shanghai | Cohort | 718 | 72,519 | A | 1 |
| [55] | Wang et al. | 2011 | Shandong | Case-control | 150 | 150 | B | 3 |
| [56] | Wang et al. | 2011 | Sichuan | Case-control | 400 | 400 | A | 1 |
| [57] | Zang et al. | 2011 | Shandong | Case-control | 348 | 1,044 | B | 2 |
| [58] | Zhang et al. | 2011 | Zhejiang | Case-control | 1,009 | 1,009 | B | 1 |
| [59] | Zheng et al. | 2011 | Tianjin | Case-control | 1,541 | 1,598 | A | 1 |
| [60] | Liao et al. | 2012 | Guangdong | Case-control | 285 | 285 | B | 1 |
| [61] | Xu et al. | 2012 | Multi-center | Case-control | 416 | 1,156 | B | 1 |
| [62] | Yu et al. | 2012 | Shandong | Case-control | 103 | 309 | B | 2 |
| [63] | Zhang et al. | 2012 | Zhejiang | Case-control | 252 | 248 | B | 1 |
| [64] | Gao et al. | 2013 | Jiangsu | Case-control | 669 | 682 | A | 2 |
| [65] | Hu et al. | 2013 | Hubei | Case-control | 196 | 211 | B | 2 |
| [66] | Tang et al. | 2013 | Guangdong | Case-control | 839 | 863 | B | 3 |
aNOS, Newcastle-Ottawa scale. A, NOS scores 8-9; B, NOS scores 5-7; C, NOS scores 1-4.
b1, only included in the meta-analysis of active smoking with breast cancer; 2, included in the meta-analysis of both active and passive smoking with breast cancer; 3, only included in the meta-analysis of passive smoking with breast cancer