ASPO Abstracts
Outdoor light at night and terminal duct lobular unit involution in the normal breast
Category: Molecular Epidemiology & Environment
Conference Year: 2021
Abstract Body:
Purpose of the study: Terminal duct lobular units (TDLUs) are structures in the breast where most
breast cancers arise, and higher TDLU counts in background normal breast tissue is associated with
a greater risk of breast cancer. Elevated outdoor light at night (LAN) has been associated with an
increased breast cancer risk in some studies, but the biologic underpinnings of this relationship are
not well defined, and its association with TDLU involution has not been studied.
Methods: From 2009-2012, women aged 18-75 donated normal breast tissue samples to the Komen
Tissue Bank and provided information on demographics, lifestyle factors, medical history, and their
residential address at the time of donation. H&E-stained FFPE breast tissue sections from 1,904
donors were analyzed for metrics of TDLU involution, including the number of TDLUs, and, for women
with ≥1 TDLU, median span and median number of acini/TDLU. Outdoor LAN from the 2010 U.S.
Defense Meteorological Satellite Program high-dynamic range data was linked to geocoded
participant addresses. Satellites provide annual nighttime ground-level illumination at ~1 km
resolution, and composite images exclude moon luminance, cloud cover, and fires. Risk ratios (RRs)
and 95% confidence intervals (CIs) for the association between LAN (quartiles and per IQR increase)
and TDLU count were determined using zero-inflated negative binomial regression models. Odds
ratios (ORs) and 95% CIs for the association between LAN, categorical TDLU span, and categorical
acini/TDLU were calculated using ordinal logistic regression.
Results: We found no association between outdoor LAN and TDLU counts (Q4 vs. Q1: RR=1.11, 95%
CI: 0.91-1.36) or LAN and acini/TDLU (Q4 vs. Q1: OR=0.89, 95% CI: 0.60-1.32). An inverse
association was observed with TDLU span (Q4 vs. Q1: OR=0.63, 95% CI: 0.43-0.91). Associations
between an IQR increase in LAN and TDLU measures were similar.
Conclusion: In this first study to examine LAN and histologic metrics of TDLU involution, LAN does not
appear to be associated with TDLU count or acini/TDLU. The apparent inverse association between
LAN and TDLU span requires further exploration. Future studies are needed to uncover mechanisms
underlying the relation of LAN with breast cancer risk.
Keywords: outdoor light at night, terminal duct lobular unit involution, breast cancer