Antibody drug conjugates (ADCs) are novel medications that combine monoclonal antibodies with cytotoxic payloads, enabling the selective delivery of potent drugs to cancer cells expressing specific surface antigens. This targeted strategy seeks to optimize treatment effectiveness while reducing the risk of systemic toxicity, distinguishing ADCs from conventional chemotherapy. The rapid growth in ADC research has led to numerous developments and approvals for cancer treatment, with significant impacts on the management of breast cancer. ADCs like T-DXd for HER2-low disease and sacituzumab govitecan for triple negative breast cancer (TNBC) have provided valuable options for challenging subtypes of breast cancer. However, essential questions still need to be addressed, including the optimal order of ADCs amidst the growing number of newly developed ones and strategies to overcome resistance mechanisms. Preclinical studies have shed light on potential resistance mechanisms, emphasizing the potential benefit of combinational approaches with other agents such as immune checkpoint inhibitors (ICIs) and targeted tyrosine kinase inhibitors (TKIs) to enhance treatment effectiveness. Additionally, personalized approaches based on molecular profiling hold promise in tailoring ADC treatments to individual tumors, identifying unique molecular markers for each patient to optimize treatment efficacy while minimizing side effects.

Size selection via filtration offers an antigen-independent approach for the enrichment of rare cell populations in blood of cancer patients. We evaluated the performance of a novel approach for multiplex rare cell detection in blood samples from metastatic breast (n = 19) and lung cancer patients (n = 21), and healthy controls (n = 30) using an automated microfluidic filtration and multiplex immunoassay strategy. Captured cells were enumerated after sequential staining for specific markers to identify circulating tumor cells (CTCs), circulating mesenchymal cells (CMCs), putative circulating stem cells (CSCs), and circulating endothelial cells (CECs). Preclinical validation experiments using cancer cells spiked into healthy blood demonstrated high recovery rate (mean = 85%) and reproducibility of the assay. In clinical studies, CTCs and CMCs were detected in 35% and 58% of cancer patients, respectively, and were largely absent from healthy controls (3%, p = 0.001). Mean levels of CTCs were significantly higher in breast than in lung cancer patients (p = 0.03). Fifty-three percent (53%) of cancer patients harbored putative CSCs, while none were detectable in healthy controls (p<0.0001). In contrast, CECs were observed in both cancer and control groups. Direct comparison of CellSearch^® vs. our microfluidic filter method revealed moderate correlation (R² = 0.46, kappa = 0.47). Serial blood analysis in breast cancer patients demonstrated the feasibility of monitoring circulating rare cell populations over time. Simultaneous assessment of CTCs, CMCs, CSCs and CECs may provide new tools to study mechanisms of disease progression and treatment response/resistance.

The emergence of CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for hormone receptor-positive breast cancer. These agents have demonstrated significant clinical benefits in terms of both progression-free survival and overall survival. However, resistance to CDK4/6 inhibitors remains a challenge, limiting their long-term efficacy. Understanding the complex mechanisms driving resistance is crucial for the development of novel therapeutic strategies and the improvement of patient outcomes. Translational research efforts, such as preclinical models and biomarker studies, offer valuable insight into resistance mechanisms and may guide the identification of novel combination therapies. This review paper aims to outline the reported mechanisms underlying CDK4/6 inhibitor resistance, drawing insights from both clinical data and translational research in order to help direct the future of treatment for hormone receptor-positive metastatic breast cancer.

Background. Sarcoma of the breast is a rare malignancy with heterogeneous histology. Angiosarcoma, including secondary angiosarcoma from previous radiation, is the most common type of sarcoma of the breast. Other types of sarcomas of the breast have limited clinical and survival information. Methods. We obtained clinicopathological data and survival outcomes from the patients with sarcoma of the breast, excluding angiosarcoma, that were registered in the National Cancer Database (NCDB) from 2004 to 2016. The treatment patterns and prognostic factors were analyzed. Results. A total of 991 patients had sarcoma of the breast other than angiosarcoma. The most common histology was spindle cell sarcoma (13.4%), followed by leiomyosarcoma (11.7%) and giant cell sarcoma (10.1%). Surgical resection was performed in 894 out of 991 patients (90.2%), including R0 resection achieved in 781 (87.4%). The patients who received surgery showed better survival than the patients without surgery regardless of radiation therapy. When radiation was added to the surgical management, the OS (overall survival) benefit was marginally significant (hazard ratio 1.30 (CI 1.01–1.67), ). Adding chemotherapy did not improve OS. Conclusions. Surgical resection seems to be the most important treatment modality in sarcoma of the breast from the analysis of a large database. Radiation therapy added a minor survival benefit to the patients who received surgical resection. Systemic chemotherapy did not play a clear role in sarcoma of the breast.

Breast cancer is a heterogeneous group of diseases characterized by diverse subtypes. Currently, the classification of breast cancer is based on the status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2). In addition to these receptors, the presence of the androgen receptor (AR) in breast cancer cells adds a layer of complexity to our understanding of the disease. The role of AR in breast cancer is intricate, as it can alter diverse signaling pathways in the presence of different hormone receptors (HRs). This complex interplay between signaling pathways affects patient outcomes and prognosis, and the presence of AR has a significant effect. While AR positivity is common in breast cancer, the efficacy of utilizing AR blockade as a monotherapy has been limited, demonstrating only modest results. To address this challenge, substantial efforts have been directed toward comprehending the intricacies of AR’s role and pathways in breast cancer development in the hope of understanding its utility as a biomarker or drug target. Multiple ongoing clinical trials are currently investigating combination treatments involving AR inhibitors and other agents to disrupt oncogenic signaling pathways and their crosstalk. Particularly in the context of triple-negative breast cancer (TNBC), where targeted therapeutic options are lacking, extensive research efforts have been dedicated to exploring the potential of AR-related interventions. This review aims to provide an overview of the various breast cancer subtypes with AR signaling mechanisms, and ongoing clinical trials that hold the potential to reshape future clinical approaches.

The systemic treatment of breast cancer has evolved remarkably over the past decades. With the introduction of immune checkpoint inhibitors (ICIs), clinical outcomes for solid tumor malignancies have significantly improved. However, in breast cancer, the indication for ICIs is currently limited to triple-negative breast cancer (TNBC) only. In high-risk luminal B hormone receptor-positive (HR+) breast cancer (BC) and HER2-positive (HER2+) BC, modest efficacy of ICI and chemotherapy combinations were identified in the neoadjuvant setting. To address the unmet need, several novel immunotherapy strategies are being tested in ongoing clinical trials as summarized in the current review: bispecific antibodies, chimeric antigen receptor T-cell therapy (CAR-T), T-cell receptors (TCRs), tumor-infiltrating lymphocytes (TILs), tumor vaccines, and oncolytic virus therapy.