Abstract
Quantitative second-harmonic generation imaging is employed to assess stromal collagen in normal, hyperplastic, dysplastic, and malignant breast tissues. The cellular scale organization is quantified using Fourier transform-second harmonic generation imaging (FT-SHG), while the molecular scale organization is quantified using polarization-resolved second-harmonic generation measurements (P-SHG). In the case of FT-SHG, we apply a parameter that quantifies the regularity in collagen fiber orientation and find that malignant tissue contains locally aligned fibers compared to other tissue conditions. Alternatively, using P-SHG we calculate the ratio of tensor elements (d15/d31, d22/d31, and d33/d31) of the second-order susceptibility χ2 for collagen fibers in breast biopsies. In particular, d15/d31 shows potential differences across the tissue pathology. We also find that trigonal symmetry (3m) is a more appropriate model to describe collagen fibers in malignant tissues as opposed to the conventionally used hexagonal symmetry (C6). This novel method of targeting collagen fibers using a combination of two quantitative SHG techniques, FT-SHG and P-SHG, holds promise for breast tissue analysis and applications to characterizing cancer in a manner that is compatible with clinical practice.
Highlights
Breast cancer is both a leading cause of cancer deaths and among the most frequently diagnosed cancers in women worldwide [1]
Most diagnostic and mechanistic studies in breast cancers focus on epithelial cells and significantly less work has been reported on the role of surrounding stroma and its extracellular matrix (ECM)
The corresponding second-harmonic generation (SHG) images are shown alongside the H&E images in which the green color provides a measurable signal and black areas indicate regions without measurable signal
Summary
Breast cancer is both a leading cause of cancer deaths and among the most frequently diagnosed cancers in women worldwide [1]. Though there are more cells in hyperplastic tissue, cellular structure and tissue morphology is similar to normal tissue In dysplasia, both the cells and their organization are abnormal while neoplasia can be benign, potentially malignant (pre-cancer), or malignant (cancer). The ECM predominantly contains type I fibrillar collagen [14], which has been recognized as being important for the initiation and progression of breast cancer [15,16,17]. Despite these promising results, the lack of analytical techniques to image the ECM is a major barrier to quantifying stromal role in breast cancer progression and, potentially, to a diagnostic protocol
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