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Background About 50% of all primary breast cancers show a low-level expression of HER2 (HER2-low), defined as immunohistochemically 1+ or 2+ and lack of HER2 gene amplification measured by in situ hybridization. This low HER2 expression is a promising new target for antibody–drug conjugates (ADCs) currently under investigation. Until now, little is known about the frequency and the prognostic value of low HER2-expression in metastatic breast cancer (MBC). Patients and methods The MBC-Registry of the Austrian Study Group of Medical Tumor Therapy (AGMT) is a multicenter nationwide ongoing registry for MBC patients in Austria. Unadjusted, univariate survival probabilities of progression-free survival (PFS) and overall survival (OS) were calculated by the Kaplan–Meier method and compared by the log-rank test. Multivariable adjusted hazard ratios were estimated by Cox regression models. In this analysis, only patients with known HER2 status and available survival data were included. Results As of 11/15/2020, 1,973 patients were included in the AGMT-MBC-Registry. Out of 1,729 evaluable patients, 351 (20.3%) were HER2-positive, 608 (35.2%) were HER2-low and 770 (44.5%) were completely HER2-negative (HER2-0). Low HER2-expression was markedly more frequent in the hormone-receptor(HR)+ subgroup compared to the triple-negative subgroup (40% vs. 23%). In multivariable analysis, low HER2 expression did not significantly influence OS neither in the HR+ (HR 0.89; 95% CI 0.74–1.05; P  = 0.171) nor in the triple-negative subgroup (HR 0.92; 95% CI 0.68–1.25; P  = 0.585), when compared to completely HER2-negative disease. Similar results were observed when HER2 IHC 2+ patients were compared to IHC 1+ or 0 patients. Conclusion Low-HER2 expression did not have any impact on prognosis of metastatic breast cancer in this real-world population.

Background Triple-negative breast cancer (TN) is more aggressive than other subtypes of breast cancer and has a lower survival rate. Furthermore, detailed biological information about the disease is lacking. This study investigated characteristics of metabolic pathways in TN. Methods We performed the metabolome analysis of 74 breast cancer tissues and the corresponding normal breast tissues using LC/MS. Furthermore, we classified the breast cancer tissues into ER-positive, PgR-positive, HER2-negative breast cancer (EP+H-) and TN, and then the differences in their metabolic pathways were investigated. The RT-PCR and immunostaining were carried out to examine the expression of ELOVL1, 2, 3, 4, 5, 6, and 7. Results We identified 142 of hydrophilic metabolites and 278 of hydrophobic lipid metabolites in breast tissues. We found the differences between breast cancer and normal breast tissues in choline metabolism, glutamine metabolism, lipid metabolism, and so on. Most characteristic of comparison between EP+H- and TN were differences in fatty acid metabolism was which were related to the elongation of very long chain fatty acids were detected between TN and EP+H-. Real-time RT-PCR showed that the mRNA expression levels of ELOVL1, 5, and 6 were significantly upregulated by 8.5-, 4.6- and 7.0-fold, respectively, in the TN tumors compared with their levels in the corresponding normal breast tissue samples. Similarly, the mRNA expression levels of ELOVL1, 5, and 6 were also significantly higher in the EP+H- tissues than in the corresponding normal breast tissues (by 4.9-, 3.4-, and 2.1-fold, respectively). The mRNA expression level of ELOVL6 was 2.6-fold higher in the TN tumors than in the EP+H- tumors. During immunostaining, the TN and EP+H- tumors demonstrated stronger ELOVL1 and 6 staining than the corresponding normal breast tissues, but ELOVL5 was not stained strongly in the TN or EP+H- tumors. Furthermore, the TN tumors exhibited stronger ELOVL1 and 6 staining than the EP+H- tumors. Conclusions Marked differences in fatty acid metabolism pathways, including those related to ELOVL1 and 6, were detected between TN and EP+H-, and it was suggested that ELOVL1 and 6-related fatty acid metabolism pathways may be targets for therapies against TN.

Background: For estrogen receptor–positive (ER+)/human epidermal growth factor receptor 2–negative (HER2–) advanced breast cancer (ABC), the current standard first-line treatment includes an aromatase inhibitor in combination with a cyclin-dependent kinase 4/6 inhibitor. When resistance occurs, often related to the occurrence of ESR1 mutations, selective estrogen receptor modulators or degraders (SERDs) may be used, alone or in combination regimens. Amcenestrant (SAR439859), an optimized oral SERD, has shown clinical antitumor activity in combination with palbociclib in patients with ER+/HER2– ABC and, as monotherapy, in patients with and without ESR1 mutations. Here, we describe the study design of AMEERA-5, an ongoing, prospective, phase 3, randomized, double-blind, multinational study comparing the efficacy and safety of amcenestrant plus palbociclib versus letrozole plus palbociclib in patients with advanced (locoregional recurrent or metastatic) ER+/HER2– breast cancer. Methods: Patients are pre-/postmenopausal women and men with no prior systemic therapy for ABC. The planned enrollment is 1066 patients. Patients are randomized 1:1 to either amcenestrant 200 mg plus palbociclib 125 mg or letrozole 2.5 mg plus palbociclib 125 mg. Amcenestrant, letrozole, and their matching placebos are taken once daily continuously; palbociclib is taken once daily for 21 days, followed by 7 days off-treatment for a 28-day cycle. Treatment continues until disease progression, unacceptable toxicity, or decision to stop treatment. Pre-/perimenopausal women and men receive goserelin subcutaneously. Randomization is stratified by de novo metastatic disease, menopausal status, and visceral metastases. The primary endpoint is progression-free survival. The key secondary endpoint is overall survival; others are safety, pharmacokinetics, and quality of life. Conclusions: AMEERA-5 is evaluating the efficacy and safety of amcenestrant in combination with palbociclib as first-line therapy in pre-/postmenopausal women and men with ER+/HER2– ABC. ClinicalTrials Identifier: NCT04478266.

Aim To improve patient selection for neoadjuvant endocrine therapy (NET), signal transduction pathway profiles of estrogen receptor (ER)-, androgen receptor (AR), were studied and compared to standard immunohistochemistry (IHC) in postmenopausal patients with HR+ (IHC ER ≥ 50%, progesterone receptor any), HER2- breast cancer of the NEOLBC trial (NCT03283384). Methods After two weeks of NET with letrozole, patients with Ki67 (Ki67-2 W) ≥ 1% IHC were randomized to receive letrozole + ribociclib or standard chemotherapy until surgery, while patients with Ki67-2 W < 1% continued NET (letrozole monotherapy). Baseline, two week- and resection FFPE samples of 82 patients were analyzed using mRNA-based OncoSIGNal profiling test, providing the pathway activity score (PAS). Results Despite samples being ER-IHC ≥ 50%, the ER-PAS varied over a range of 32–78 (scale from 0 to 100) with 20% of the patients showing low ER-PAS (32–45; similar to triple negative breast cancer tissue). At 2 weeks, 89% (73/82) of the patients showed a decreased ER-PAS (11.6 ± 8.6) compared to baseline ( p < 0.001), whereas ER-IHC remained unchanged. Patients with complete response (RECIST1.1) appeared to have a higher ER-PAS at baseline compared to those with stable disease ( p = 0.03), ROC analysis confirmed ER-PAS at baseline as an acceptable predictive factor for MRI response (AUC ≥ 0.7). Lastly, baseline and 2-week pathway activity profiling could identify targetable escape mechanisms for NET non-responders, which could improve personalized treatment strategies. Conclusion ER IHC+ does not correlate to ER-PAS and ER-PAS is a more dynamic marker that appears to reflect variable NET response more accurately than IHC. Key points ER-PAS is an acceptable predictive factor for clinical response assessed by MRI (RECIST 1.1) in patients with HR+/HER2- postmenopausal breast cancer patients treated with NET. Non-elevated ER-PAS at baseline was predictive to have Ki67 ≥ 1% in 83% (15/18), despite ER-IHC positivity. OncoSIGNal pathway activity profiling shows potential at identifying alternative actionable pathways such as PI3K-AKT-mTOR, Hedgehog and MAPK-RAS-ERK for patients with early NET resistance.

Background Although endocrine therapies, alone or in combination with CDK4/6 inhibitors, have led to notable improvements in the treatment of estrogen receptor-positive (ER+) breast cancer, progression is inevitable for most patients. We report dose escalation and expansion data from a trial of H3B-6545 (a novel selective ER covalent antagonist that inactivates wild-type and mutant ERα) in women with locally advanced/metastatic ER+, HER2-negative breast cancer (BC). Methods This study was a multicenter, open-label, phase 1/2 trial. Women ≥ 18 years of age with ER+, HER2 − BC whose disease progressed on their most recent therapy were eligible. Prior therapy must have included at least 2 hormonal therapies (HTs), or 1 HT and 1 chemotherapy, or 1 HT and a CDK4/6 inhibitor. In phase 1, H3B-6545 was administered orally once daily at doses of 100–600 mg. In phase 2, the efficacy of the recommended phase 2 dose (RP2D) determined in phase 1 was examined in additional patients, including those with/without ERα mutation. The primary endpoints were RP2D determination (phase 1) and objective response rate (ORR) (phase 2, investigator-assessed per RECIST v1.1). Additional primary endpoints (phase 2) included progression-free survival (PFS) and overall survival (OS), per Kaplan-Meier estimates. Results 151 Patients were treated across phases. During phase 1, 2 DLTs (drug eruption and fatigue, both grade 3) were observed at the 600 mg dose, and 450 mg was deemed the RP2D. In the total population (phases 1 and 2), all patients experienced ≥ 1 treatment-emergent adverse event (TEAE), and 50.3% had grade 3–4 TEAEs, with no grade 5 TEAEs observed. In phase 1, the overall ORR was 7.5% (95% CI 1.6–20.4). The ORR in all response-evaluable patients treated at 450 mg ( n  = 94) was 20.2% (95% CI 12.6–29.8). Patients with clonal ESR1 Y537S mutation had an ORR of 32.1% (95% CI 15.9–52.4). For all patients who received H3B-6545 450 mg, median PFS was 4.6 months (95% CI 3.5–6.7) and median OS was 21.5 months (95% CI 16.6–25.5). Conclusions Results suggest that H3B-6545 may be further investigated as an endocrine therapy option for patients with previously treated metastatic ER + BC. Trial registration NCT03250676. Registered August 11, 2017.

PurposeThe monarchE trial showed that the addition of abemaciclib improves efficacy in patients with high-risk early breast cancer (EBC). We analyzed the long-term outcomes of a population similar to the monarchE trial to put into context the potential benefit of abemaciclib.MethodsHR-positive/HER2-negative EBC patients eligible for the monarchE study were selected from 3 adjuvant clinical trials and a breast cancer registry. Patients with ≥ 4 positive axillary lymph nodes (N +) or 1–3 N + with tumor size ≥ 5 cm and/or histologic grade 3 and/or Ki67 ≥ 20%, who had undergone surgery with curative intent and had received anthracyclines ± taxanes and endocrine therapy in the neoadjuvant and /or adjuvant setting were included. We performed analysis of Invasive Disease-Free Survival (iDFS), Distant Disease-Free Survival (dDFS) and Overall Survival (OS) at 5 and 10 years, as well as yearly (up to 10) of Invasive Relapse Rate (IRR), Distant Relapse Rate (DRR) and Death Rate (DR).ResultsA total of 1,617 patients were analyzed from the GEICAM-9906 (312), GEICAM-2003–10 (210), and GEICAM-2006–10 (160) trials plus 935 from El Álamo IV. With a median follow-up of 10.1 years, the 5 and 10 years iDFS rates were 75.2% and 57.0%, respectively. The dDFS and OS rates at 5 years were 77.4% and 88.8% and the respective figures at 10 years were 59.7% and 70.9%.ConclusionsThis data points out the need for new therapies for those patients. A longer follow-up of the monarchE study to see the real final benefit with abemaciclib is warranted.Trial registrationClinTrials.gov: GEICAM/9906: NCT00129922; GEICAM/ 2003-10: NCT00129935 and GEICAM/ 2006-10: NCT00543127.

Identifying high-risk of late recurrence (beyond 10 years) in patients with hormone receptor-positive HER2-negative early breast cancer (EBC) is crucial. The Clinical Treatment Score post-5 years (CTS5) score assesses recurrence risk after 5 years of endocrine therapy (ET). This study validated CTS5 as a prognostic tool for late recurrence by examining its association with Distant Recurrence-Free Survival using GEICAM study data and evaluating model calibration. We retrospectively analyzed 5739 hormone receptor-positive HER2-negative EBC patients from the El Álamo IV registry (N = 3509, diagnosed between 2002 and 2005) and 4 adjuvant GEICAM studies (N = 2680, conducted between 1996 and 2006). All patients were distant recurrence-free and alive 5 years after starting adjuvant ET. The CTS5 classified 43.9% of patients as low-risk, 32.2% as intermediate-risk, and 23.9% as high-risk. Significant differences in DR were observed: hazard ratio (HR) for intermediate- vs. low-risk was 2.55 (95% CI, 1.85-3.51, P < .0001), and HR for high- vs. low-risk was 5.77 (95% CI, 4.28-7.78, P < .0001). Similar results were found across subgroups by menopausal status, duration of adjuvant ET, and prior adjuvant chemotherapy (CT). Calibration showed CTS5 overestimated DR rates in low-risk (P = .0314) and high-risk (P < .0001) patients compared to observed rates. The CTS5 categorized patients based on late DR risk regardless of menopausal status, ET duration, or CT treatment. However, the model tended to overestimate events, particularly in high-risk groups, especially among those treated with ET for less than 60 months or not receiving CT.

Patients with HR+/HER2- metastatic breast cancer (MBC) whose cancers have progressed despite conventional therapies represent an unmet clinical need. Trop-2, a transmembrane calcium signal transducer, is highly expressed in MBC and plays a role in tumor growth and progression. Sacituzumab govitecan (SG) is a novel antibody–drug conjugate comprising an Trop-2 antibody coupled to SN-38, the active metabolite of irinotecan, via a unique hydrolyzable linker. SG has demonstrated promising activity in a Phase I/II IMMU-132-01 basket study in heavily pretreated solid tumors, including HR+/HER2- MBC. We describe the registrational Phase III TROPiCS-02 study (NCT03901339), evaluating SG versus treatment of physician’s choice in HR+/HER2- MBC. Trial registration number: NCT03901339.

Background Palbociclib is an oral small-molecule inhibitor of cyclin-dependent kinases 4 and 6. In the randomized, open-label, phase II PALOMA-1/TRIO-18 trial, palbociclib in combination with letrozole improved progression-free survival (PFS) compared with letrozole alone as first-line treatment of estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, advanced breast cancer (20.2 months versus 10.2 months; hazard ratio (HR) = 0.488, 95 % confidence interval (CI) 0.319–0.748; one-sided p  = 0.0004). Grade 3–4 neutropenia was the most common adverse event (AE) in the palbociclib + letrozole arm. We now present efficacy and safety analyses based on several specific patient and tumor characteristics, and present in detail the clinical patterns of neutropenia observed in the palbociclib + letrozole arm of the overall safety population. Methods Postmenopausal women ( n  = 165) with ER+, HER2-negative, advanced breast cancer who had not received any systemic treatment for their advanced disease were randomized 1:1 to receive either palbociclib in combination with letrozole or letrozole alone. Treatment continued until disease progression, unacceptable toxicity, consent withdrawal, or death. The primary endpoint was PFS. We now analyze the difference in PFS for the treatment populations by subgroups, including age, histological type, history of prior neoadjuvant/adjuvant systemic treatment, and sites of distant metastasis, using the Kaplan-Meier method. HR and 95 % CI are derived from a Cox proportional hazards regression model. Results A clinically meaningful improvement in median PFS and clinical benefit response (CBR) rate was seen with palbociclib + letrozole in every subgroup evaluated. Grade 3–4 neutropenia was the most common AE with palbociclib + letrozole in all subgroups. Analysis of the frequency of neutropenia by grade during the first six cycles of treatment showed that there was a downward trend in Grade 3–4 neutropenia over time. Among those who experienced Grade 3–4 neutropenia, 71.7 % had no overlapping infections of any grade and none had overlapping Grade 3–4 infections. Conclusion The magnitude of clinical benefit seen with the addition of palbociclib to letrozole in improving both median PFS and CBR rate is consistent in nearly all subgroups analyzed, and consistent with that seen in the overall study population. The safety profile of the combination treatment in all subgroups was also comparable to that in the overall safety population of the study.

Opinion Statement Navigating the complex landscape of breast cancer treatment involves distinct strategies for luminal and triple-negative subtypes. While neoadjuvant chemotherapy historically dominates the approach for aggressive triple-negative tumors, recent evidence highlights the transformative impact of immunotherapy, alongside chemotherapy, in reshaping treatment paradigms. In luminal cancers, endocrine therapy, notably aromatase inhibitors, demonstrates promising outcomes in postmenopausal patients with low-grade luminal A tumors. However, integrating targeted therapies like CDK4/6 inhibitors in neoadjuvant setting remains inconclusive. Identifying predictive factors for treatment response, especially in luminal tumors, poses a challenge, emphasizing the necessity for ongoing research. A multidisciplinary approach, tailored to individual patient profiles, is crucial for maximizing efficacy while minimizing toxicity. As we strive to optimize breast cancer management, a comprehensive understanding of the distinct characteristics and treatment implications of luminal and triple-negative subtypes, including the transformative role of immunotherapy, is essential for informed decision-making and personalized care.