Breast cancer cells disseminate through TIE2/MENACalc/MENAINV-dependent cancer cell intravasation sites, called tumor microenvironment of metastasis (TMEM), which are clinically validated as prognostic markers of metastasis in breast cancer patients. Using fixed tissue and intravital imaging of a PyMT murine model and patient-derived xenografts, we show that chemotherapy increases the density and activity of TMEM sites and Mena expression and promotes distant metastasis. Moreover, in the residual breast cancers of patients treated with neoadjuvant paclitaxel after doxorubicin plus cyclophosphamide, TMEM score and its mechanistically connected MENAINV isoform expression pattern were both increased, suggesting that chemotherapy, despite decreasing tumor size, increases the risk of metastatic dissemination. Chemotherapy-induced TMEM activity and cancer cell dissemination were reversed by either administration of the TIE2 inhibitor rebastinib or knockdown of the MENA gene. Our results indicate that TMEM score increases and MENA isoform expression pattern changes with chemotherapy and can be used in predicting prometastatic changes in response to chemotherapy. Furthermore, inhibitors of TMEM function may improve clinical benefits of chemotherapy in the neoadjuvant setting or in metastatic disease.

Anthracycline-based regimens have been an important treatment component for patients with breast cancer. As demonstrated in the last Early Breast Cancer Trialists' Collaborative Group (EBCTCG) meta-analysis, anthracycline-based regimens decrease breast cancer mortality by 20-30%. Anthracycline toxicities include the rare-but potential morbid-cardiotoxicity or leukemogenic effect, and the almost universal-but very distressing-alopecia. Due to potential toxicities, and large number of patients being exposed, several worldwide trials have re-examined the role of anthracycline-based regimens in the management of breast cancer. Current literature supports that anthracyclines are not required for all patients with breast cancer and should be avoided in those with high cardiac risk. Recent results from the ABC trials suggest that anthracyclines should not be spared for patients with triple negative breast cancer (regardless of axillary node involvement) or HER2-/ER+ with significant node involvement. Based on current literature, for HER2-negative patients with low-risk breast cancer, anthracyclines could be spared with regimens such as cyclophosphamide, methotrexate, and fluorouracil (CMF) or docetaxel and cyclophosphamide (TC). Patients with intermediate or high-risk breast cancer should be considered for anthracycline-based regimens based on other factors such as age, comorbidities, tumor grade, lymphovascular invasion, and genomic profiling. Patients with HER2-positive breast cancer with low risk could be treated with paclitaxel and trastuzumab. For the remaining patients with HER2 overexpression, while docetaxel, carboplatin, and trastuzumab (TCH) has demonstrated to improve disease-free survival (DFS), anthracycline-containing regimens should be discussed, especially for those with very high-risk breast cancer. Although several biomarkers, such as topoisomerase II (TOP2A) and chromosome 17 centromeric duplication (Ch17CEP) have been proposed to predict benefit from anthracycline regimens, further research is required to delineate their proper utility in the clinical setting.

Metastatic dissemination in breast cancer is regulated by specialized intravasation sites called “tumor microenvironment of metastasis” (TMEM) doorways, composed of a tumor cell expressing the actin-regulatory protein Mena, a perivascular macrophage, and an endothelial cell, all in stable physical contact. High TMEM doorway number is associated with an increased risk of distant metastasis in human breast cancer and mouse models of breast carcinoma. Here, we developed a novel magnetic resonance imaging (MRI) methodology, called TMEM Activity-MRI, to detect TMEM-associated vascular openings that serve as the portal of entry for cancer cell intravasation and metastatic dissemination. We demonstrate that TMEM Activity-MRI correlates with primary tumor TMEM doorway counts in both breast cancer patients and mouse models, including MMTV-PyMT and patient-derived xenograft models. In addition, TMEM Activity-MRI is reduced in mouse models upon treatment with rebastinib, a specific and potent TMEM doorway inhibitor. TMEM Activity-MRI is an assay that specifically measures TMEM-associated vascular opening (TAVO) events in the tumor microenvironment, and as such, can be utilized in mechanistic studies investigating molecular pathways of cancer cell dissemination and metastasis. Finally, we demonstrate that TMEM Activity-MRI increases upon treatment with paclitaxel in mouse models, consistent with prior observations that chemotherapy enhances TMEM doorway assembly and activity in human breast cancer. Our findings suggest that TMEM Activity-MRI is a promising precision medicine tool for localized breast cancer that could be used as a non-invasive test to determine metastatic risk and serve as an intermediate pharmacodynamic biomarker to monitor therapeutic response to agents that block TMEM doorway-mediated dissemination.