Introduction: Endocrine therapies targeting cell proliferation and survival mediated by estrogen receptor α (ERα) are among the most effective systemic treatments for ERα-positive breast cancer. However, most tumors initially responsive to these therapies acquire resistance through mechanisms that involve ERα transcriptional regulatory plasticity. Herein we identify VAV3 as a critical component in this process. Methods: A cell-based chemical compound screen was carried out to identify therapeutic strategies against resistance to endocrine therapy. Binding to ERα was evaluated by molecular docking analyses, an agonist fluoligand assay and short hairpin (sh)RNA–mediated protein depletion. Microarray analyses were performed to identify altered gene expression. Western blot analysis of signaling and proliferation markers, and shRNA-mediated protein depletion in viability and clonogenic assays, were performed to delineate the role of VAV3. Genetic variation in VAV3 was assessed for association with the response to tamoxifen. Immunohistochemical analyses of VAV3 were carried out to determine its association with therapeutic response and different tumor markers. An analysis of gene expression association with drug sensitivity was carried out to identify a potential therapeutic approach based on differential VAV3 expression. Results: The compound YC-1 was found to comparatively reduce the viability of cell models of acquired resistance. This effect was probably not due to activation of its canonical target (soluble guanylyl cyclase), but instead was likely a result of binding to ERα. VAV3 was selectively reduced upon exposure to YC-1 or ERα depletion, and, accordingly, VAV3 depletion comparatively reduced the viability of cell models of acquired resistance. In the clinical scenario, germline variation in VAV3 was associated with the response to tamoxifen in Japanese breast cancer patients (rs10494071 combined P value = 8.4 × 10⁻⁴). The allele association combined with gene expression analyses indicated that low VAV3 expression predicts better clinical outcome. Conversely, high nuclear VAV3 expression in tumor cells was associated with poorer endocrine therapy response. Based on VAV3 expression levels and the response to erlotinib in cancer cell lines, targeting EGFR signaling may be a promising therapeutic strategy. Conclusions: This study proposes VAV3 as a biomarker and a rationale for its use as a signaling target to prevent and/or overcome resistance to endocrine therapy in breast cancer.

Paget disease of the breast represents a cutaneous manifestation of an underlying breast malignancy. The rare finding of a pigmented Paget disease mimicking melanoma represents a diagnostic problem. We report a case of a pigmented lesion involving the breast nipple with an underlying infiltrating breast carcinoma, and we describe the clinical presentation, histological findings, and immunohistochemical features with a review of reported cases.

Background/Objectives: Tumor-infiltrating lymphocytes (TILs) are recognized predictors of response to neoadjuvant chemotherapy (NACT) and prognosis in breast cancer, particularly in triple-negative (TN) and HER2-positive subtypes. However, the additional predictive value of morphological features of the inflammatory infiltrate beyond TIL quantification is not fully established. We aimed to assess the predictive value of TILs for response to NACT in breast cancer and to determine whether morphological characteristics of the inflammatory infiltrate enhance predictive accuracy. Methods: We analyzed 477 patients with stage II–III breast cancer treated with NACT between 2009 and 2016. Diagnostic core needle biopsies were prospectively re-evaluated. TILs were quantified according to International TILs Working Group recommendations. Morphological features of the infiltrate, including cell composition (lymphocytic vs. plasma cell-rich), heterogeneity, and localization, were evaluated using standardized criteria. Pathologic complete response (pCR) was defined as absence of invasive tumor in the breast and in the axillary lymph nodes (ypT0/Tis ypN0). Univariate and multivariate logistic regression analyses were performed to assess the predictive value of TILs (quantitative and morphological assessment) to achieve pCR for the entire cohort and by surrogate molecular subtype. Results: A TIL cutoff of >20% was identified as optimal for predicting pCR. High TILs were significantly associated with high-grade tumors, elevatedKi67, HER2-positive and TN subtypes, presence of plasma cells, and intraepithelial and heterogeneous infiltrates. In the overall cohort, TILs > 20% significantly increased the likelihood of pCR (OR 3.9, 95%IC 2.5–6.0, p < 0.001) and was an independent predictor of pCR. A combined variable incorporating TIL level and homogeneity improved predictive performance, with homogeneously high TILs emerging as a strong predictor of pCR (OR 5.521, 95%CI 3.174–9.603, p < 0.01). Plasma cell-rich and intraepithelial infiltrates were also associated with higher pCR rates (respectively, OR 2.7, 95%CI 1.5–5.0, p = 0.001 and OR 2.8, 95%CI 1.6–5.0, p < 0.001). Subtype-specific analyses confirmed the predictive value of TILs in TN tumors, but not in HER2-positive ones. Notably, in luminal B-like tumors, high TILs were the only independent predictor of response (OR 17.982, 95%CI 3.115–103.815, p = 0.001). Conclusions: TIL assessment on routine H&E-stained biopsies is a robust predictor of response to NACT in breast cancer that is readily available, cost-neutral and does not require additional techniques. Integration of simple morphological features significantly enhances predictive accuracy and may refine treatment stratification, particularly in luminal B-like tumors.

Hormone receptor-positive, HER2-negative breast cancers are often poorly infiltrated by immune cells and derive limited benefit from current immunotherapy strategies. Here, using paired tumour samples from the randomised window-of-opportunity D-BIOMARK trial ( NCT03691311 ), we investigated the immunomodulatory effects of denosumab in early luminal breast cancer. Short-term preoperative denosumab reduced tumour-cell proliferative transcriptional programs and immunosuppressive features of the local tumour microenvironment, enhancing innate and adaptive immune activation and altering circulating cytokine profiles. High-resolution spatial transcriptomics revealed coordinated remodelling of tumour, immune, fibroblast and endothelial compartments after treatment. Denosumab reduced immune–tumour spatial separation and enhanced T cell activation, accompanied by a shift from matrix-associated tumour programs towards increased tumour–T cell communication. Copy number-informed tumour-state inference further identified a reduced representation of genomically complex, immune-poor tumour subclones after treatment. Together, these findings identify denosumab as a modulator of tumour–microenvironment crosstalk and support RANKL blockade as a strategy to render immune-poor luminal breast tumours more permissive to immune engagement.