PM_2.5, vegetation density, and childhood cancer: a case-control registry-based study from Texas 1995-2011

Background: Air pollution is positively associated with some childhood cancers, whereas greenness is inversely associated with some adult cancers. The interplay between air pollution and greenness in childhood cancer etiology is unclear. We estimated the association between early-life air pollution and greenness exposure and childhood cancer in Texas (1995 to 2011). Methods: We included 6101 cancer cases and 109 762 controls (aged 0 to 16 years). We linked residential birth address to census tract annual average fine particulate matter <2.5 mg/m³ (PM_2.5) and Normalized Difference Vegetation Index (NDVI). We estimated odds ratios (ORs) and 95% confidence intervals (CIs) between PM_2.5/NDVI interquartile range increases and cancer. We assessed statistical interaction between PM_2.5 and NDVI (likelihood ratio tests). Results: Increasing residential early-life PM_2.5 exposure was associated with all childhood cancers (OR ¼ 1.10, 95% CI ¼ 1.06 to 1.15), lymphoid leukemias (OR ¼ 1.15, 95% CI ¼ 1.07 to 1.23), Hodgkin lymphomas (OR ¼ 1.27, 95% CI ¼ 1.02 to 1.58), non-Hodgkin lymphomas (OR ¼ 1.24, 95% CI ¼ 1.02 to 1.51), ependymoma (OR ¼ 1.27, 95% CI ¼ 1.01 to 1.60), and others. Increasing NDVI exposure was inversely associated with ependymoma (0- to 4-year-old OR ¼ 0.75, 95% CI ¼ 0.58 to 0.97) and medulloblastoma (OR ¼ 0.75, 95% CI ¼ 0.62 to 0.91) but positively associated with malignant melanoma (OR ¼ 1.75, 95% CI ¼ 1.23 to 2.47) and Langerhans cell histiocytosis (OR ¼ 1.56, 95% CI ¼ 1.07 to 2.28). There was evidence of statistical interaction between NDVI and PM_2.5 (P < .04) for all cancers. Conclusion: Increasing early-life exposure to PM_2.5 increased the risk of childhood cancers. NDVI decreased the risk of 2 cancers yet increased the risk of others. These findings highlight the complexity between PM_2.5 and NDVI in cancer etiology.