PURPOSE:The aim of this study was to evaluate the safety and feasibility of ipatasertib combined with trastuzumab and pertuzumab (HP) as maintenance therapy after first-line treatment in patients with HER2-positive metastatic breast cancer harboring PIK3CA mutations (PIK3CAmut). PATIENTS AND METHODS:This prospective, multicenter, single-arm, phase Ib study evaluated the safety and preliminary efficacy of ipatasertib, an AKT inhibitor, combined with HP, with or without endocrine therapy as maintainance therapy, in patients with unresectable locally advanced or metastatic PIK3CAmut, HER2-positive breast cancer following first-line induction chemotherapy and HP. RESULTS:Seventeen patients were enrolled, with a median follow-up of 27.7 months. During the dose-selection phase, ipatasertib at 400 mg daily (21 days on and 7 days off) with standard HP was established as the recommended phase II dosage. This decision was based on the absence of dose-limiting toxicities in the first six patients treated at this dosage during the initial 28-day cycle, which constituted the primary endpoint. Grade 3 treatment-related adverse events (TRAE) occurred in seven patients (41.2%), most commonly diarrhea and nausea. Two (11.8%) reported four serious TRAE (diarrhea, vomiting, ischemic stroke, and pneumonitis, one case each) related to ipatasertib, from which they recovered. The confirmed overall response rate was 31.1% [95% confidence interval (CI), 12.1%-58.5%], clinical benefit rate 84.6% (95% CI, 53.7%-97.3%), and median progression-free survival 16.4 months (95% CI, 9.4-NR); 47.3% of patients were progression free at 18 months. CONCLUSIONS:These results support ipatasertib plus HP as a safe and promising maintenance strategy for HER2-positive breast tumors harboring PIK3CAmut.

PURPOSE:Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors plus endocrine therapy (ET) represents the standard first-line treatment for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HER2-negative) advanced breast cancer (ABC). However, there is no definitive consensus on the preferred second-line treatment option. The PALMIRA trial investigated whether palbociclib rechallenge with an alternative ET would improve the antitumor activity in patients progressing after a first-line palbociclib-containing regimen. METHODS:This international, randomized, open-label, phase II study enrolled 198 patients with hormone receptor-positive/HER2-negative ABC with disease progression after first-line palbociclib plus ET (aromatase inhibitor or fulvestrant). Patients were eligible if they showed clinical benefit to the previous regimen (response or stable disease ≥24 weeks) or had progressed on a palbociclib-based therapy in the adjuvant setting. Patients were randomly assigned (2:1 ratio) to either palbociclib rechallenge plus second-line ET (fulvestrant or letrozole) or second-line ET alone. Stratification factors were previous ET and visceral involvement. The primary end point was investigator-assessed progression-free survival (PFS). RESULTS:Between April 2019 and October 2022, 136 and 62 patients were randomly assigned to palbociclib plus ET or ET alone, respectively. Median investigator-assessed PFS was 4.9 months (95% CI, 3.6 to 6.1) with palbociclib plus ET versus 3.6 months (95% CI, 2.5 to 4.2) with ET alone (hazard ratio, 0.84 [95% CI, 0.66 to 1.07]; P = .149). Grade ≥3 treatment-emergent adverse events were higher with palbociclib plus ET (47.4% v 10.0%), without new safety signals. CONCLUSION:Palbociclib rechallenge plus an alternative ET did not significantly improve PFS compared with ET alone in patients with hormone receptor-positive/HER2-negative ABC progressing on a first-line palbociclib-based ET regimen.

Background: Neoadjuvant endocrine therapy (NET) in oestrogen receptor-positive /HER2-negative breast cancer (ER+/HER2- BC) allows real-time evaluation of treatment sensitivity by monitoring tumour response and offers the opportunity of personalised therapy. However, the lack of reproducible biomarkers to assess response and long-term prognosis after NET is a significant barrier to increase its indications. Methods: In this study we searched for clinically relevant molecular reporters of response to NET in a multicentre population of ER+/HER2- BC patients (n = 87) by using: PAM50 gene expression panel and immunohistochemical evaluation of key proteins involved in tumorigenesis. Results: Our PAM50 analyses show that tumours changing from luminal A to normal-like subtype after NET presented better radiological and pathological tumour responses, a significant larger decrease in Ki67 at surgery, lower preoperative endocrine prognostic index score (PEPI) and lower tumour cellularity size (TCS) than those with persistent luminal A status. Patients with the highest response to NET showed the largest decrease in PAM50-derived risk of recurrence (ROR) following NET. In addition, the percentage of p53 positive cells was associated with decreased response to NET. Conclusions: Our findings highlight the change of intrinsic subtype from luminal A to normal-like after NET as a putative biomarker characterising the patient population that obtains the highest benefit from NET. Our study also suggests that changes in PAM50-derived ROR score and p53 evaluation could also help to identify those patients. Thus, this study uncovers potential biomarkers of response to NET and prognosis, which should be validated in independent cohorts, helping to the implementation of NET in the clinical practice.

Supplementary Table S1. Selection Criteria; Supplementary Table S2. Recruiting Sites, Principal Investigators, and Patient Numbers; Supplementary Table S3. Study Members; Supplementary Table S4. List of antibodies used for immunohistochemistry analysis; Supplementary Table S5. Cutoff values for the quantitative assessment of biomarkers by immunohistochemistry; Supplementary Table S6. The 77-gene panel by the AVENIO ctDNA Expanded Kit used for targeted NGS on plasma samples; Supplementary Table S7. Representativeness of study participants; Supplementary Table S8. Association of baseline clinical and pathologic characteristics of trial participants included in the efficacy analysis with clinical benefit; Supplementary Table S9. Relative dose intensity and drug discontinuation; Supplementary Table S10. All causality AEs according to NCI-CTCAE version 4.0.3 occurring in at least 5% of the patients; Supplementary Table S11. Adverse events of special interest according to NCI-CTCAE version 4.0.3; Supplementary Table S12. Baseline clinical and pathologic characteristics of trial participants included in the retinoblastoma and signature subsets; Supplementary Table S13. Tumor best response according to RECIST version 1.1 of trial participants included in the retinoblastoma and signature subsets; Supplementary Table S14. Association of biomarkers and composite signatures with clinical benefit.

Summary of all adverse events according to NCI-CTCAE version 4.0.3.

Kaplan-Meier analyses of investigator-assessed progression-free survival and overall survival in the efficacy population.

The level of mutant and wild-type circulating DNA in baseline plasma samples by patient.

(A) Longitudinal ctDNA quantification during study treatment. (B) Variations of ctDNA during study treatment. (C, D) Kaplan-Meier analyses of investigator-assessed progression-free survival according to the ctDNA detection after 2 weeks and 12 weeks of study treatment.

The amplification or overexpression of human epidermal growth factor receptor 2 (HER2) defines a breast cancer subtype, which benefits from neoadjuvant HER2-targeted therapy. However, at least 40% of patients respond poorly or do not respond to treatment. We analyzed the main genomic alterations of 64 HER2+ patients by next-generation sequencing to identify new predictors of response and correlate them with clinicopathological parameters. We also compared the genomic alterations between primary and residual tumors after neoadjuvant treatment. The TP53 gene was the most frequently mutated gene, and in combination with ERBB2 overexpression, the 2 were predictive of residual cancer burden (P = .001). Furthermore, the combination of their immunohistochemical counterpart (p53 mutant and score 3+ for HER2) can predict complete pathological response and the grade of response (P = .038 and P = .031, respectively). Therefore, p53 could be included in the initial panel of breast cancer biomarkers to help therapeutic decision-making in HER2+ cases.

Background: Human epidermal growth factor receptor 2 (HER2)-low has emerged as a potential new entity in breast cancer (BC). Data on this subset are limited, and prognostic results are controversial, evidencing the need of further data in a BC real-world cohort. Methods: Patients with HER2-negative stage I–III BC diagnosed between 2006 and 2016 were retrospectively reviewed in a single cohort from the Catalan Institute of Oncology Badalona. Demographics and clinicopathological characteristics were examined via medical charts/electronic health records. We aim to describe and compare HER2-0/HER2-low populations through Chi-square or Fisher test, and explore its prognostic impact using Kaplan–Meier curves and Cox regression models. Results: From a cohort of 1755 BC patients, 1401 invasive HER2-negative, stage I–III cases were evaluated. 87% were hormone receptor (HR)-positive versus 13% triple negative (TNBC). Overall, 43% were HER2-0 and 57% HER2-low (61% immunohistochemistry (IHC) 1+ and 39% IHC 2+). Comparing HER2-low versus HER2-0, HER2-low showed higher proportion of estrogen receptor (ER)-positive (91.6% vs 79.9%, p ⩽ 0.001) and progesterone receptor (PR)-positive (79.8% vs 68.9%, p ⩽ 0.001) cases. HER2-0 exhibited higher proportion of TNBC (20.1% vs 8.4%, p = 0.001), grade III tumors (28.8% vs 23.5%, p = 0.039), and higher Ki67 median value (26.47% vs 23.88%, p = 0.041). HER2-low was associated with longer time to distant recurrence (TTDR) compared to HER2-0 (67.8 vs 54.1 months; p = 0.015) and better BC-related survival (19.2 vs 16.3 years; p = 0.033). In the multivariable analysis, HER2-low was not an independent prognostic factor for TTDR and BC-related survival. ER expression showed a strong association with longer TTDR (Hazard Ratio: 0.425, p ⩽ 0.001) and improved BC-related survival (Hazard Ratio: 0.380, p ⩽ 0.001). PR expression was also associated with longer TTDR (Hazard Ratio: 0.496, p ⩽ 0.001), and improved BC-related survival (Hazard Ratio: 0.488, p ⩽ 0.001). Histological grade III was significantly associated with shorter TTDR (Hazard Ratio: 1.737, p = 0.002). Positive nodal status was the strongest factor correlated with worse BC-related survival (Hazard Ratio: 2.747, p ⩽ 0.001). Conclusion: HER2-low was significantly associated with HR-positive disease, whereas HER2-0 group had higher incidence of TNBC, histological grade III and higher Ki67%. Although HER2-low group was associated with longer TTDR and improved BC-related survival, these findings could be explained by the greater proportion of favorable prognostic features in this subgroup compared to HER2-0.

Triple-negative breast cancer (TNBC) is a highly aggressive subtype with limited therapeutic options, leading to higher relapse rates and mortality. Identifying prognostic biomarkers like caveolin-1 (CAV1) is crucial for personalized treatment. CAV1 influences tumor progression and chemotherapy response, particularly through its interaction with the tumor microenvironment (TME) and cancer metabolism. Understanding the prognostic value of CAV1 in different cellular compartments is essential for its clinical application in TNBC. In the methods section CAV1 gene expression in TNBC was evaluated using in silico analysis, followed by the immunohistochemical staining of tumor cytoplasm (cCAV1) and stromal cells (sCAV1) in 58 early-stage TNBC patients. Statistical analyses were performed to correlate CAV1 expression with clinicopathological features and survival. In the results section, in silico analysis revealed higher CAV1 expression in TNBC, correlating with shorter overall survival. In the patient samples, cCAV1 was observed in 10.3% of cases, and was associated with larger tumors, higher grades, and poorer prognoses. sCAV1 was detected in 42% of cases, associated with less proliferative and less aggressive tumors, but did not significantly impact prognoses. In conclusion, cCAV1 expression is a significant prognostic marker in early-stage TNBC, highlighting the importance of assessing CAV1 in different cellular compartments. Further research is needed to explore the mechanisms and clinical implications of cCAV1.

Cyclin-dependent kinases 4/6 inhibitors (CDK 4/6i) combined with endocrine therapy have become the gold standard in hormone receptor-positive (HR +) HER2-negative (HER2-) metastatic breast cancer (MBC). However, there is a significant lack of data regarding the efficacy and safety of these treatments in elderly patients. We present the results of a real-world data (RWD) cohort stratified by age at treatment initiation (≥ 70 years compared to patients < 70 years). Clinico-pathological data of HR + HER2- MBC patients who were candidates for CDK4/6i therapy between January 2017 and December 2020 at the Institut Català d'Oncologia (Spain) were retrospectively collected. The primary goal was to assess Progression-Free Survival (PFS), Overall Survival (OS), and safety outcomes within this patient population. A total of 274 patients with MBC who received CDK4/6i treatment were included in the study. Among them, 84 patients (30.8

BACKGROUND:The effect of the addition of cyclin-dependent kinases 4 and 6 inhibitors to endocrine therapy in terms of molecular downstaging remains undetermined. Switching from a high-risk to a low risk Recurrence Score (RS) group could provide useful information to identify patients who might not require chemotherapy. The purpose of this study was to assess the biological and clinical activity of letrozole plus palbociclib as neoadjuvant treatment for patients with hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative early breast cancer with an initial Oncotype DX RS ≥18. PATIENTS AND METHODS:Participants were women aged ≥18 years with HR-positive/HER2-negative, Ki67 ≥ 20%, stage II-IIIB early breast cancer with a baseline RS ≥18. Eligible patients with a pretreatment RS 18-25 (cohort A) and 26-100 (cohort B) received six 28-day cycles of letrozole (2.5 mg per day; plus goserelin if pre- or perimenopausal) plus palbociclib (125 mg per day; 3/1 schedule) before surgery. The primary endpoint for both cohorts was the proportion of patients who achieved an RS ≤25 at surgery or a pathological complete response (pCR). RESULTS:A total of 67 patients were enrolled, among which 65 were assessable for the primary endpoint (32 patients in cohort A and 33 in cohort B). At surgery, 22 (68.8%) patients in cohort A and 18 (54.5%) patients in cohort B had an RS ≤25 or a pCR [only 1 (3.0%) patient in cohort B], meeting the primary endpoint in cohort B (P < 0.01), but not in cohort A (P = 0.98). No new safety signals were identified. CONCLUSIONS:The efficacy of neoadjuvant treatment with letrozole plus palbociclib does not seem to depend on pretreatment RS for patients with RS ≥18. However, around half of patients with HR-positive/HER2-negative early breast cancer with an RS 26-100 at baseline achieved molecular downstaging with this regimen.

577 Background: HER-2 low has emerged as a potential new entity in breast cancer (BC). Data of this subset is still limited and prognostic results are controversial, suggesting HER2-low does not represent a distinct biological subtype. HER2-low account for up to 50% of BC, representing a potential therapeutic target with encouraging results in the metastatic setting. Hence, we pretend to analyze clinical characteristics of this subset to elucidate commented points. Methods: Confirmed HER2-negative BC patients (p) diagnosed between 2006-2017 were retrospectively reviewed in a single center study, in ICO-Badalona. HER2-positive and in situ carcinomas were excluded, and p were classified as HER2-low and HER2-0. The prevalence of HER2-low versus HER2-0 among p, originally scored as HER2-negative, was measured. Demographics and clinicopathological characteristics were examined and compared via medical charts/electronic health records. We aim to describe HER2-0/HER2-low populations, and explore its prognostic impact, using Kaplan-Meyer and Cox regression models. Results: From 1451 infiltrating HER2-negative BC p, 87% were hormone receptor (HR)-positive vs 13% triple negative (TNBC). Overall, 43% were HER2-0 and 57% HER2-low (61% IHC 1+ and 39% IHC 2+). Comparing HER2-0 vs HER2-low, the latest showed significant higher proportion of ER-positive (80% vs 91.7%, p = < 0.001) and PR-positive (69.3% vs 79.1%, p = < 0.001) cases, but there were no differences between HER2-low 1+ vs 2+. HER2-0 exhibited higher proportion of TNBC p (20% vs 8.3%, p = 0.001), grade III tumors (28.8% vs 23.5%, p = 0.036) and higher Ki67 median value (26.47% vs 23.88%, p = 0.041). No significant differences were observed in median age at diagnosis, menopausal status, clinical stage, clinical nodal status, histological subtype, time to recurrence, time to local recurrence and overall survival (OS). HER2-low presented longer time to distant recurrence (TDR) compared to HER2-0 (67.8 vs 54.1 months, p = 0.015) and better BC-related OS (19.2 vs 16.3 years, p = 0.033). However, in the multivariate analysis, considering HER2, ER, PR, histological grade and nodal status, PR showed the strongest association with longer TDR (HR: 0.69; 95%CI 0.54-0.89, p = 0.004); and positive nodal status was the strongest factor related to worse BC-related OS (HR: 2.97; CI 2.10-4.21, p = 0.000). No statistical differences in TDR and BC-related OS were observed between HER2 1+ vs 2+ populations. Conclusions: HER2-low was significantly associated to HR-positive disease whereas TNBC, histological grade III and higher Ki67% were more represented in HER2-0 group. Although HER2-0 was related to worse TDR and BC-related OS, these findings could be explained by the presence of an enriched population in worse prognostic features, as suggested by multivariate analysis. New therapies for HER2-0 disease are an unmet medical need.