Abstract 841: Fine particulate matter exposure during breast cancer treatment among older women associated with increased mortality
Authors: Bates Benjamin , Nethery Rachel , Rua Melanie , Iyer Hari , Bandera Elisa , Setoguchi Soko 
Published: March 2024

Abstract
Background: Fine Particulate Matter (PM2.5) is associated with higher mortality among people with chronic conditions. Breast cancer (BC) survivors may be particularly vulnerable during cancer treatment. We assessed the association between PM2.5 during 9-months following BC diagnosis and all-cause and BC-mortality using policy relevant PM2.5 cut-offs.
Methods: Using SEER-Medicare linked with a high-resolution model-based PM2.5 by residential zipcode (2007-2016), we assembled a cohort of women ≥66 years with incident stage I-IV BC. We assessed PM2.5 exposure, categorized as &lt;8 µg/m3 (low), 8-12 µg/m3 (moderate) and &gt;12 µg/m3 (high—above air quality standard), and types of cancer treatments (surgery [SX], chemotherapy [CTX], radiation therapy [RTX]) during a 9-month landmark period. We identified all-cause and BC death within 5 years of diagnosis. We fit multivariable Cox proportional hazard models to assess associations with PM2.5 exposure adjusting for individual-level characteristics (demographics, tumor characteristics, comorbidities), neighborhood SES, SEER state, and long-term PM2.5 exposure. We also evaluated the association between PM2.5 exposure and mortality by treatment types (SX, SX + RTX, SX + CTX, SX + RTX + CTX, and RTX and/or CTX). We used multiple imputation to account for missing variables (race, ER status, HER2 status, grade).
Results: Among 72,798 women (mean age 75 years, 83% white, 56% stage I, 32% II, 9.2% III, 2.9% IV), 41%, 32%, 13%, 8.4%, and 5.1% received SX + RTX, SX only, SX + Chemo + RTX, SX + Chemo, and CTX and/or RTX. The mean PM2.5 level was 8.8 µg/m3 [36%, 52% and 11% were exposed to &lt;8, 8-12, and &gt;12, respectively]. We observed 12,163 all-cause and 4,729 BC deaths during follow-up. Compared to those exposed to low levels, higher levels of PM2.5 exposure were associated with increased all-cause mortality for both moderate PM2.5 [HR 1.03 (95%CI:1.00-1.05)] and high PM2.5 [HR 1.09 (95%CI: 1.06-1.14)] but not BC-specific mortality. Among treatment subgroups, PM2.5 was associated with higher all-cause mortality in SX+RTX for moderate [HR 1.24 (95%CI:1.18-1.32)] and high PM2.5 [HR 1.36 (95%CI: 1.25-1.48)] and SX+RTX+CTX for high PM2.5 [HR 1.33 (95%CI: 1.17-1.51)]. There were no association between moderate/high PM2.5 with all-cause mortality in SX only and SX+CTX. Among the SX+RTX subgroup, BC-specific mortality was elevated for both moderate [HR 1.50 (95%CI:1.35-1.66)] and high PM2.5 [HR 1.81 (95%CI: 1.55-2.12)].
Conclusion: Even below EPA regulatory thresholds (PM2.5 &lt;12 µg/m3), we observed increased risk of death in BC survivors who had high PM2.5 exposure during treatment period. The elevated mortality primarily occurred among women who received RTX and was present for all-cause and BC-specific mortality. The potential interaction between RTX and PM2.5 exposure, even after adjusting for tumor subtype and stage, warrants further evaluation.
Citation Format: Benjamin Bates, Rachel Nethery, Melanie Rua, Hari Iyer, Elisa Bandera, Soko Setoguchi. Fine particulate matter exposure during breast cancer treatment among older women associated with increased mortality [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 841.