Second-Harmonic Generation Imaging Reveals Changes in Breast Tumor Collagen Induced by Neoadjuvant Chemotherapy

SIMPLE SUMMARY: Most breast cancer deaths are due to metastases. Neoadjuvant, or pre-surgical, chemotherapy is given to shrink select aggressive breast cancers but can have unpleasant side effects and induce changes in the tumor microenvironment. This pre-surgical chemotherapy also increases one signature in breast tumors that is prognostic of metastasis. We assessed the effect of neoadjuvant chemotherapy on two other prognostic signatures derived from the tumor collagen: second-harmonic generation directionality and fiber alignment. We found that directionality changes in the tumor bulk of two breast cancer subtypes but not in the tumor/stromal interface. Fiber alignment is increased in only one breast cancer subtype. The results indicate that neoadjuvant chemotherapy affects tumor extracellular collagen in a manner specific to breast tumor subtype and alters some, but not all, prognostic signatures. This may impact the clinical utility of these signatures. ABSTRACT: Breast cancer is the most common invasive cancer in women, with most deaths attributed to metastases. Neoadjuvant chemotherapy (NACT) may be prescribed prior to surgical removal of the tumor for subsets of breast cancer patients but can have diverse undesired and off-target effects, including the increased appearance of the ‘tumor microenvironment of metastasis’, image-based multicellular signatures that are prognostic of breast tumor metastasis. To assess whether NACT can induce changes in two other image-based prognostic/predictive signatures derived from tumor collagen, we quantified second-harmonic generation (SHG) directionality and fiber alignment in formalin-fixed, paraffin-embedded sections of core needle biopsies and primary tumor excisions from 22 human epidermal growth factor receptor 2-overexpressing (HER2+) and 22 triple-negative breast cancers. In both subtypes, we found that SHG directionality (i.e., the forward-to-backward scattering ratio, or F/B) is increased by NACT in the bulk of the tumor, but not the adjacent tumor-stroma interface. Overall collagen fiber alignment is increased by NACT in triple-negative but not HER2+ breast tumors. These results suggest that NACT impacts the collagenous extracellular matrix in a complex and subtype-specific manner, with some prognostic features being unchanged while others are altered in a manner suggestive of a more metastatic phenotype.