6th International Workshop on Breast Densitometry and Breast ...

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6 th <strong>International</strong> <strong>Workshop</strong> on Breast Densitometry
and Breast Cancer Risk Assessment
EXPLORING A RELATIONSHIP BETWEEN EXTRACELLULAR MATRIX STIFFNESS
AND MAMMOGRAPHIC DENSITY IN THE HUMAN BREAST
Irene Acerbi 1,2 , Alfred Au 2 , Ori Maller 1,2 , Quanming Shi 2,3 , Jan Liphardt 2,3 , Yunn-yi Chen 4 , Shelley
Hwang 5 , Valerie M. Weaver 1,2,6,7,8
1 Department of Surgery and Center for Bioengineering and Tissue Regeneration, University of California,
San Francisco, CA, USA; 2 Bay Area Physical Sciences in Oncology Center, Berkeley, CA, USA
3 Department of Physics, University of California, Berkeley, CA, USA; 4 UCSF Carol Buck Breast Cancer
Center, San Francisco, CA, USA; 5 Department of Pathology, University of California, San Francisco, CA,
USA; 6 Department of Surgery, Duke University, Durham, NC, USA; 7 Institute for Regeneration Medicine,
University of California San Francisco, CA, USA; 8 Department of Bioengineering and Therapeutic
Sciences, University of California, San Francisco, CA, USA; 9 Department of Anatomy, University of
California, San Francisco, CA, USA
Mammographic density (MD) is associated with high collagen content in the extracellular matrix
(ECM) and greater risk to malignancy. Data from our group and others have highlighted the importance
of mechanical cues from the ECM in breast tissue homeostasis and tumor progression [Paszek et al.,
Cancer Cell 2005; Levental et al., Cell, 2009; reviewed in Yu et al., Trends Cell Biol, 2010].
Nevertheless, a role for ECM stiffness in tumor cell initiation is unknown. In this study, we hypothesize
that high MD correlates with stiffer breast ECM and enhances women’s risk for breast cancer compared
to low MD.
To test this hypothesis, we studied breast tissues obtained through prophylactic mastectomy from
women with high MD (BIRADS 4) versus low (BIRADS 1). From each surgically excised breast,
samples of 0.5cm x 0.5cm x 1cm dimension were removed from the retroareolar region and from 4
peripheral quadrants. Sample sections were subjected to biophysical, morphological and biochemical
analysis. Biophysical analysis included the application of Atomic Force Microscopy (AFM) to obtain an
extensive force map of distinct anatomical regions of the ECM associated with the intra-lobular and interlobular
ECM. ECM architecture has been analyzed using two photons and SIM-POL imaging coupled
with picrosirius staining, polarized light imaging and image quantification. Biochemical and
morphological analysis consisted of immunohistochemistry for markers that detect mechano-signaling in
the epithelium and stromal fibroblasts, and H&E to visualize cellular and ECM organization.
We studied samples from the different 5 quadrants of a same breast. We found that the ECM
associated with the upper outer region, was in tendency stiffer (AFM) and had higher tension (SIMPOL
birefringence) than the other peripheral quadrants. We show heterogeneity within multiple regions of the
same breast, with the upper outer region, where most tumors occur, contained linearized collagen fibrils.
Most invasive breast cancers arise from the ductal epithelium. Therefore, we studied the ECM
associated with the Terminal Ductal Lobular Units (TDLU): inter-lobular ECM (among the TLDU), and
intra-lobular ECM (within the TDLU). The inter-lobular ECM of the breast contained linearized collagen
fibrils and was relatively stiffer. In contrast, we found that the intra-lobular ECM associated with the
TDLU in the breast contained less linearized collagen fibrils and was compliant.
In a small cohort, breast tissues from of the upper outer region were examine to directly explore
the relationship between extracellular matrix stiffness and high MD across a patient population. Our
preliminary data suggest an increase in collagen abundance and higher content of linearized collagen
fibers adjacent to TLDUs were associated with high MD. Our future efforts will focus on increasing the
size of the cohort to further establish a correlative relationship between MD and ECM stiffness. We will
also examine the significance of this relationship in tumor cell initiation.
ABSTRACTS
Acknowledgements: supported by W81XWH-05-1-0330 and R01 CA138818-01A1 to VMW, 1U01 ES019458-01
to VMW and ZW, and P50 CA 58207 to JG, VW, SH and LC, U54CA143836-01 to JL and VW, and Susan G.
Komen for the Cure PSF12230246 to IA.
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