Breast cancer is the most commonly diagnosed malignancy worldwide, with molecular subtypes following distinct clinical trajectories. While Luminal A breast cancers are typically indolent, a subset enriched in α-smooth muscle actin (α-SMA)-positive cancer-associated fibroblasts (CAFs) exhibits aggressive behavior, facilitating tumor invasion. However, the biophysical mechanisms by which CAFs drive invasion and extracellular matrix (ECM) remodeling remain unclear. In addition, the temporal and spatial dynamics of CAF interactions with the collagen matrix and cancer cell spheroids remain unknown, raising the question of whether these processes follow a deterministic sequence or occur stochastically. To address this, we conducted histological analysis of Luminal A tumors, which revealed variation in CAF, cancer cell, and ECM organization at tumor boundaries. To assess the impact of CAF on cancer cell invasion, we use a 3D in-vitro model co-embedding 19TT breast CAF and MCF7 luminal breast cancer spheroids within a three-dimensional (3D) collagen-I hydrogel and performed time-lapse imaging. We demonstrate that inter-spheroid distance critically determines 19TT CAF-induced MCF7 spheroid behavior. Moreover, we showed that CAF-mediated collagen matrix remodeling and degradation precede the observed MCF7 spheroid disruption and are critical in promoting cancer cell spheroid expansion and cell dissemination. While broad-spectrum matrix metalloproteinase inhibition suppressed CAF-driven collagen degradation and MCF7 spheroid expansion, it did not prevent ECM remodeling, CAF migration, or single-cell dissemination of cancer cell spheroids. Furthermore, a complementary heterospheroid model revealed similar ECM remodeling and invasion dynamics despite the altered cellular arrangement of cancer cells and CAFs. Our findings enhance our understanding of the relationship between CAF activity and collagen matrix remodeling processes that promote cancer cell invasion, providing insights into the potential therapeutic benefits of targeting CAFs in breast cancer treatment. Statement of Significance This research provides key insights into breast cancer-associated fibroblasts (CAFs) mediated remodeling of the extracellular matrix (ECM) and subsequent breast cancer cell dissemination and invasion. Herein, we demonstrated that CAFs remodel collagen fibres before migration and matrix metalloproteinase (MMP)-mediated degradation. Using a 3D in-vitro model, we showed that distinct mechanisms govern cancer cell spheroid expansion and single-cell dissemination: while expansion depends on collagen matrix integrity, dissemination relies on CAF-driven collagen remodeling. These findings advance our understanding of the relationship between CAF activity and collagen matrix remodeling processes that promote cancer cell invasion, providing insights into the potential therapeutic benefits of targeting CAFs in breast cancer treatment. ... Read more

Background: Colorectal cancer is highly prevalent. The stromal tumour microenvironment significantly influences tumour behaviour, and cancer-associated fibroblasts (CAFs), as major component of tumour stroma, are increasingly studied. Specifically, CAF-marker fibroblast activation protein (FAP) is gaining interest as tracer for imaging using radiolabelled FAP-inhibitor (FAPI). We describe patterns of FAP-expression, and associations to intratumoural stroma amount, establishing a biological background and potential future reference to pathology assessment.

Materials and methods: Archival histological material from 125 stage-II/III CRC patients was collected. Haematoxylin-and-eosin staining was performed to determine the tumour-stroma ratio (TSR), indicating stromal percentages in primary tumours, lymph nodes (LNs) and biopsies. On immunohistochemistry stains, FAP-expression was semiquantitatively scored as little-no, heterogeneous, or moderate-high expression. Correlation of TSR and FAP-expression with Chi-square testing was assessed. Other patterns were also described, e.g. tumour epithelial FAP-expression.

Results: In total, 93 patients (40 stage-III colon [CC], 53 stage-II/III RC) were included. Correlation between 41 (44 %) stroma-high CRC (18/40 CC, 45 %; 23/53 RC, 43 %) with high FAP-expression was not significant (P = 0.428 CRC; P = 0.470 CC; P = 0.615 RC). The majority of CRC had any FAP-expression (78 CRC, 84 %), mostly the invasive front, and in most associated LN metastases (87 % CRC tumour-positive LN). However, FAP-expression was often heterogeneous, even staining healthy colon and lymphoid tissue.

Conclusions: CRCs and LN metastases generally express FAP, but levels vary significantly between and within tumours and have no direct correlation with TSR. Care has to be taken translating FAPI-PET/CT results with e.g. disease extent and activity, emphasizing the importance of multidisciplinary approach. ... Read more