Hormone receptor-positive/HER2-negative breast cancer (BC) is the most common subtype of BC and typically occurs as an early, operable disease. In patients receiving neoadjuvant chemotherapy (NACT), pathological complete response (pCR) is rare and multiple efforts have been made to predict disease recurrence. We developed a framework to predict pCR using clinicopathological characteristics widely available at diagnosis. The machine learning (ML) models were trained to predict pCR (n = 463), evaluated in an internal validation cohort (n = 109) and validated in an external validation cohort (n = 151). The best model was an Elastic Net, which achieved an area under the curve (AUC) of respectively 0.86 and 0.81. Our results highlight how simpler models using few input variables can be as valuable as more complex ML architectures. Our model is freely available and can be used to enhance the stratification of BC patients receiving NACT, providing a framework for the development of risk-adapted clinical trials.

Background/Objectives: HER2-positive breast cancer (HER2⁺BC) is an aggressive subtype, with neoadjuvant treatment (NAT) aiming to achieve a pathological complete response (pCR) to improve long-term outcomes. Trastuzumab emtansine (T-DM1) has been established as the standard of care in the adjuvant setting for HER2⁺BC patients who do not obtain pCR. The ATD study aimed to evaluate the real-world tolerability of T-DM1 in this setting. The secondary objective was to assess the effectiveness. Methods: This was a multicenter, retrospective study across 24 Italian oncology centers, including 410 patients with HER2⁺BC treated with adjuvant T-DM1 following a lack of pCR after NAT. Patient characteristics, NAT regimens, and surgical outcomes were recorded. Tolerability was assessed by documenting adverse events (AEs) according to the CTCAE (v5.0). Preliminary effectiveness was evaluated in terms of relapse-free survival (RFS) and overall survival (OS). Results: Overall, 228 patients (55.6%) experienced at least one AE related to T-DM1, with 4.9% experiencing grade 3 or higher AEs. The most common AEs were hepatotoxicity (18.5%) and thrombocytopenia (17.6%). T-DM1 was discontinued in 10.0% of patients due to toxicity. After a median follow-up of 25 months, 31 relapse events (7.6%) and 22 deaths (5.4%) were reported. The preliminary incidence of RFS and OS events was similar between patients who completed the T-DM1 course and those who discontinued it early. Conclusions: T-DM1 demonstrated a manageable safety profile, and the adverse events were consistent with those reported in randomized trials. The data are not yet sufficient to allow for a formal analysis of RFS and OS, and long-term follow-up is required.

Introduction: Radiotherapy (RT) shows potential for improving local control in cases of oligoprogressive metastatic breast cancer (mBC). This retrospective analysis aims to evaluate the advantages of RT in such a clinical scenario. Methods: We conducted a retrospective analysis including patients with mBC who received radiation therapy (RT) for up to three sites of oligoprogression while continuing systemic therapy. The study took place between January 2014 and December 2021. Our endpoints were progression-free survival after radiotherapy (PFS-AR), the rate of discontinuation of systemic therapy (RDT) at three months post-RT, and overall survival (OS). We used Cox regression analysis to perform multivariate analysis for PFS-AR. Results: Fifty-nine patients met the inclusion criteria. The PFS-AR was 13 months (95% CI 8.5–18.8 months). At three months, the RDT was 3% (two patients). A significant difference in median PFS-AR was observed between patients in the first + second-line group and those in the subsequent line group (p = 0.03). In the multivariate analysis conducted for PFS-AR, the biologically effective dose (BED) with α/β = 4 > 100 Gy emerged as the sole significant variable (p = 0.0017). The median overall survival (OS) was 24.4 months (95% CI 17–24.4 months). Conclusions: This study is the first report on the outcomes of radiotherapy in a cohort of over 50 patients with oligoprogressive metastatic breast cancer (mBC). Our findings emphasize the significant relationship between PFS-AR, the number of ongoing lines of systemic therapy, and the BED of radiotherapy.

HER2-positive/hormone-receptor-positive breast cancer represents approximately 10% of all breast cancer cases and constitutes a distinct biological entity with unique therapeutic challenges. The complex crosstalk between HER2 and estrogen receptor signaling pathways contributes to both primary and acquired resistance to anti-HER2 therapies, and the convergence of these pathways on cell cycle regulation, particularly through the cyclin D1-CDK4/6-Rb axis, has provided a compelling rationale for combining CDK4/6 inhibitors with anti-HER2 therapy. This scoping review aimed to map preclinical and clinical evidence evaluating combinations of CDK4/6 inhibitors with HER2-targeted therapy in HER2+/HR+ disease. Eligible sources included preclinical models and clinical studies assessing CDK4/6 inhibitor-based combinations with anti-HER2 therapy, identified through searches of PubMed, Embase, Cochrane Library, Web of Science and ClinicalTrials.gov. Data were charted and synthesized descriptively according to PRISMA-ScR guidelines. Preclinical studies have demonstrated synergistic antitumor activity when CDK4/6 inhibitors are combined with trastuzumab, pertuzumab, or newer HER2-targeted agents across multiple HER2+ breast cancer models. In the metastatic setting, phase II trials including MonarcHER and PATRICIA II have shown encouraging efficacy signals, while the phase III PATINA trial demonstrated a clinically meaningful 15.2-month progression-free survival benefit with palbociclib plus anti-HER2 therapy and endocrine therapy. In the neoadjuvant setting, trials including NA-PHER2 and MUKDEN-01 demonstrated marked Ki67 suppression and promising pathologic responses, supporting the exploration of chemotherapy de-escalation strategies. Despite these advances, key challenges remain including the identification of predictive biomarkers, optimal treatment sequencing, and the integration of emerging HER2-targeted agents such as trastuzumab deruxtecan. Novel CDK4/6 inhibitors including dalpiciclib and next-generation agents are expanding therapeutic options, while combination strategies incorporating CDK7 inhibition represent future therapeutic frontiers. The evolving landscape of HER2+/HR+ breast cancer treatment increasingly emphasizes precision medicine approaches that leverage cell cycle control mechanisms to overcome resistance and improve patient outcomes across all disease stages.

Adjuvant endocrine therapy for early breast cancer significantly reduces recurrence but increases bone fragility. Given limited data on denosumab (60 mg every 6 months) in premenopausal patients receiving endocrine therapy for early breast cancer, we conducted a retrospective real-world study at the Gemelli Hospital (September 2018–January 2025). A descriptive analysis was performed. The primary endpoint was to assess efficacy, evaluated by changes in bone mineral density via dual-energy X-ray absorptiometry and by monitoring bone turnover markers, particularly serum C-terminal telopeptide of type I collagen. Safety was evaluated based on adverse endocrine therapy events (osteoporotic fractures) and adverse denosumab events (osteonecrosis of the jaw). Sixty-nine patients were eligible for the study. Endocrine therapy included ovarian function suppression with exemestane (89.8%) or tamoxifen (10.1%). Baseline spinal osteoporosis decreased from 20.3% to 5.8%, osteopenia from 39.1% to 34.8%, with normal T-scores rising from 17.4% to 34.8%. Femoral improvements were similar. Serum C-terminal telopeptide of type I collagen levels (evaluated in 35.8%) showed stable reduction in 97%. Denosumab adherence was 89.9%. One osteonecrosis of the jaw case occurred (1.4%); no fractures were reported. Denosumab demonstrated efficacy in improving bone density and reducing bone turnover, with excellent adherence and favorable safety. Longer follow-up is needed to assess post-discontinuation effects.