Abstract A006: Spatial localization of Caveolin-1 protein in triple negative breast cancer is related to different molecular features
Authors: Godina Christopher , Khazaei Somayeh , Belting Mattias , Vallon-Christersson Johan , Nodin Björn , Jirström Karin , Isaksson Karolin , Bosch Ana , Jernström Helena 
Published: February 2024

Abstract
Background: Triple negative breast cancer (TNBC) is an aggressive and heterogeneous form of breast cancer with few targeted therapies and clinically used biomarkers. Caveolin-1 (CAV1) is a marker of stromal activation and vascularization. Molecular features of the tumor microenvironment (TME), important for tumor metastasis, may improve precision oncology in TNBC. CAV1 protein levels have previously been reported as a potential biomarker in breast cancer depending on their localization. Therefore, we aimed to investigate CAV1 protein levels in malignant and stromal cells of TNBC and their relation to CAV1 gene expression, clinicopathological factors, and molecular features. Methods: Tumor-specific CAV1 protein levels were evaluated with immunohistochemistry in malignant and stromal cells in tumor tissue microarrays from a cohort of 242 TNBC patients (inclusion 2010-2015, Sweden) from SCAN-B (NCT03758976). The protein levels of CAV1 in malignant and stromal cells were dichotomized as ‘strong’ (1) vs ‘negative to moderate’ (0) The CAV1 categories in malignant and stromal cells, respectively, were combined to create a joint CAV1 status with four categories: malignant/stromal cells, 0/0, 0/1, 1/0, and 1/1. Gene expression profiles from massive parallel paired-end sequencing of mRNA (RNA-seq) were available for all the tumors and from which PAM50 category and TNBC subtype were assigned. CAV1 status in malignant and stromal cells in relation to clinicopathological factors was analyzed using Chi-Square test. CAV1 mRNA expression in relation to CAV1 status in malignant and stromal cells was evaluated using Kruskal-Wallis test. Results: CAV1 status could be evaluated in 231/242 tumors. Strong CAV1 staining in malignant cells was associated with higher histological grade but no axillary lymph node involvement (both P &lt;0.007). In contrast, strong CAV1 staining in stromal cells was associated with lower histological grade but axillary lymph node involvement (both P &lt;0.001). Strong CAV1 staining in stromal cells was also associated with higher age at diagnosis (P =0.025). With regards to PAM50 subtypes, CAV1 in malignant cells was positively associated with the basal subtype while CAV1 in malignant cells was positively associated with the HER2 enriched subtype (P &lt;0.001). Depending on localization, CAV1 expression was associated with different TNBCsubtypes. CAV1 in malignant cells was positively associated with the mesenchymal and negatively associated with the immunomodulatory subtype (P &lt;0.001). CAV1 in stromal cells was positively associated with the luminal androgen (LAR) subtype (P &lt;0.001). Neither CAV1 protein levels in malignant cells nor in stromal cells were correlated with CAV1 gene expression in the tumors, and the combined CAV1 status was not associated with CAV1 gene expression. Conclusion: CAV1 protein levels in malignant cells were related to different molecular features of TNBC compared to CAV1 protein levels in stromal cells. The results suggest that depending on localization, CAV1 protein levels function as two distinct biomarkers.
Citation Format: Christopher Godina, Somayeh Khazaei, Mattias Belting, Johan Vallon-Christersson, Björn Nodin, Karin Jirström, Karolin Isaksson, Ana Bosch, Helena Jernström. Spatial localization of Caveolin-1 protein in triple negative breast cancer is related to different molecular features [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A006.