Table 2.
Particulate matter and cancer mortality in the subgroup meta-analysis of cohort studies by various factors. WHO, World Health Organization.
| Subgroups | PM2.5 | PM10 | ||||
|---|---|---|---|---|---|---|
| No. of Studies | Summary RR (95% CI) | I2 (%) | No. of Studies | Summary RR (95% CI) | I2 (%) | |
| Gender | ||||||
| Male only | 5 | 1.14 (1.00, 1.29) | 80.5 | 4 | 1.06 (0.93, 1.22) | 69.1 |
| Female only | 6 | 1.13 (1.05, 1.21) | 32.0 | 6 | 1.03 (0.92, 1.15) | 72.3 |
| Male and Female | 16 | 1.18 (1.11, 1.25) | 97.8 | 6 | 1.10 (1.05, 1.16) | 94.9 |
| Region | ||||||
| America | 11 | 1.18 (1.08, 1.29) | 97.2 | 6 | 1.05 (1.05. 1.23) | 76.5 |
| Europe | 5 | 1.16 (1.00, 1.35) | 94.9 | 4 | 1.18 (0.99, 1.41) | 95.3 |
| Asia | 3 | 1.17 (1.05, 1.30) | 85.1 | 1 | 1.05 (1.03, 1.06) | NA |
| Follow-up period | ||||||
| <10 years | 10 | 1.17 (1.07, 1.27) | 96.3 | 4 | 1.11 (0.96, 1.29) | 89.6 |
| ≥10 years | 9 | 1.19 (1.07, 1.32) | 98.1 | 9 | 1.06 (1.03, 1.09) | 82.1 |
| Mean levels of pollutant concentration according to the WHO guideline | ||||||
| Below the standard | 4 | 1.20 (1.04, 1.39) | 98.3 | 1 | 1.16 (1.04, 1.29) | NA |
| Above the standard | 12 | 1.18 (1.09, 1.28) | 91.1 | 9 | 1.09 (1.04, 1.15) | 93.1 |
| Types of cancer | ||||||
| Lung cancer | 14 | 1.14 (1.07, 1.21) | 97.1 | 9 | 1.07 (1.03, 1.11) | 83.3 |
| Cancers other than lung cancer | 5 | 1.16 (1.04, 1.30) | 90.9 | 3 | 1.05 (0.99, 1.11) | 44.1 |
| Brain cancer | 2 | 1.00 (0.84, 1.19) | 36.1 | 2 | 0.93 (0.83, 1.03) | 0.0 |
| Lymphatic & hematopoietic cancer | 2 | 1.06 (0.90, 1.25) | 10.6 | 1 | 1.04 (0.93, 1.16) | NA |
| Breast cancer | 3 | 1.60 (0.94, 2.72) | 83.4 | 2 | 1.06 (0.93, 1.21) | 64.6 |
| Liver cancer | 2 | 1.29 (1.06, 1.58) | 67.8 | 1 | 1.11 (0.84, 1.46) | NA |
| Pancreas cancer | 1 | 0.96 (0.91, 1.02) | NA | 1 | 1.05 (1.04, 1.28) | NA |
| Larynx cancer | 1 | 1.09 (0.66, 1.79) | NA | 1 | 1.27 (1.06, 1.54) | NA |
| Stomach cancer | 2 | 1.17 (0.83, 1.65) | 73.4 | 1 | 0.99 (0.84, 1.16) | NA |
| Colorectal cancer | 2 | 1.08 (1.00, 1.17) | 0.0 | 1 | 0.87 (0.71, 1.07) | NA |
| Bladder cancer | 1 | 1.32 (1.07, 1.60) | NA | 1 | 1.17 (0.88, 1.57) | NA |
| Kidney cancer | 1 | 1.35 (1.07, 1.72) | NA | 1 | 1.03 (0.84, 1.26) | NA |
| Stage of cancer | ||||||
| Localized | 3 | 1.81 (1.63, 2.01) | 74.0 | 2 | 1.20 (1.12, 1.28) | 45.1 |
| Regional | 3 | 1.47 (1.36, 1.59) | 55.2 | 2 | 1.12 (1.11, 1.13) | 0.0 |
| Metastasis | 3 | 1.17 (1.05, 1.30) | 71.2 | 2 | 1.08 (1.02, 1.14) | 49.3 |
| No. of participants | ||||||
| Small (<100,000) [15,16,17,18,22,24,25,27,32,33,35,36,39,40] | 5 | 1.22 (1.15, 1.30) | 0.0 | 6 | 1.05 (0.97, 1.13) | 77.0 |
| Large (>100,000) [7,19,20,21,23,28,29,30,31,34,37,38,41,42,43] | 14 | 1.17 (1.10, 1.24) | 98.1 | 6 | 1.11 (1.02, 1.21) | 92.8 |
| Methodological quality | ||||||
| Low quality (<8) | 9 | 1.14 (1.06, 1.22) | 98.1 | 4 | 1.09 (1.08, 1.10) | 0.0 |
| High quality (≥8) | 10 | 1.20 (1.08, 1.33) | 93.5 | 8 | 1.10 (1.01, 1.21) | 94.2 |
| Smoking status | ||||||
| Non-smokers | 3 | 1.14 (1.01, 1.28) | 0.0 | 1 | 1.66 (1.22, 2.28) | NA |
| Ex-smokers | 3 | 1.47 (1.17, 1.84) | 51.4 | |||
| Current smokers | 2 | 1.33 (1.20, 1.49) | 0.0 | |||
NA, not applicable; PM, particulate matter; RR, relative risk; WHO, world health organization.