Abstract 4216: Interactions of greenness with air pollution in relation to postmenopausal breast cancer risk in UK Biobank
Authors: Smotherman Carmen , Sprague Brian , Datta Susmita , Braithwaite Dejana , Qin Huaizhen , Yaghjyan Lusine 
Published: April 2023

Abstract
Purpose: The evidence of the association between natural vegetation, or greenness, and breast cancer (BCa) remains inconsistent, with some studies reporting possible interactions with air pollution. We previously found a positive association of particulate matter with diameters than are 10 micrometers or smaller (PM10) with BCa risk among postmenopausal women in the UK Biobank. In this study, we investigated the associations of greenness with postmenopausal BCa risk, as well as whether association of PM10 with BCa differ by the level of greenness.
Methods: This study included 155,235 postmenopausal women (6,146 with BCa) from UK Biobank, a population-based prospective cohort. Cancer diagnoses were ascertained through the linkage to the UK National Health Service Central Registers. Greenness measures (Greenspace percentage [GP], Natural environment percentage [NEP], and the Normalized Difference Vegetation Index [NDVI]) were available at baseline assessment (2006 -2010). GP and NEP coverage were calculated at 300 m and 1000 m, respectively, around participant residence locations, while the mean NDVI was calculated within a 500 m residential buffer of each UK Biobank participant. Annual averages for PM10 were available from 2007 and 2010. Information on BCa risk factors was collected at baseline. We used Cox proportional hazards regression to evaluate associations between greenness (continuous as well as quartiles) and BCa risk, while adjusting for BCa risk factors. Next, we examined associations for year-specific and cumulative average PM10 exposure measures (per 5 µg/m3) within each stratum of greenness measure. Interactions between PM10 and greenness measures were assessed by including an interaction term in the main models.
Results: BCa risk increased by 29% per one unit increase in NDVI (Hazard ratio [HR]=1.29, 95% CI 1.03, 1.61). Compared to women in the lowest NDVI quartile, women with higher levels of NDVI had higher risk of BCa (HR=1.10, 95% CI 1.01, 1.21 for 2nd quartile, HR=1.10, 95% CI 1.00, 1.20 for 3rd quartile, and HR=1.13, 95% CI 1.04, 1.24 for 4th quartile, p-trend=0.012). No significant associations were found for any other greenness measure in relation to BCa risk. We found a significant interaction between NDVI and cumulative average PM10 exposure (p&lt;0.0001). The association of PM10 cumulative average with BCa risk was stronger at lower levels of NDVI (HR per 5 µg/m3=1.12, 95% CI 1.07, 1.17 for 1st quartile) compared to higher levels of NDVI (HR=1.04, 95% CI 1.02, 1.07 for 4th quartile). We found no interactions with other greenness measures.
Conclusions: We found a positive association of NDVI with BCa risk and an interaction between cumulative average PM10 and NDVI, with stronger positive association of cumulative average PM10 exposure with postmenopausal BCa risk at lower compared to higher levels of greenness.
Citation Format: Carmen Smotherman, Brian Sprague, Susmita Datta, Dejana Braithwaite, Huaizhen Qin, Lusine Yaghjyan. Interactions of greenness with air pollution in relation to postmenopausal breast cancer risk in UK Biobank. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4216.