Bellet, Meritxell

Abstract Background: Invasive lobular carcinoma (ILC) accounts for up to 15% of breast cancer (BC) cases and has distinct clinical and biological features compared to invasive carcinoma of no special type (IBC-NST). Prior studies, including PENELOPE-B, suggested greater benefit from adjuvant palbociclib (palbo) in ILC. We assessed the prognostic and predictive value of histology in patients (pts) treated with endocrine therapy (ET) ± palbo. Methods: PALLAS is a global, phase III trial in which pts with stage II-III, HR+/HER2− BC were randomized to 2 years (y) of adjuvant palbo + ET or ET alone. Pts with IBC-NST or pure ILC per local pathology assessment were included. Endpoints included invasive disease-free (IDFS; primary), distant recurrence-free (DRFS), locoregional recurrence-free (LRRFS), and overall survival (OS). Prognostic value was assessed using univariable and multivariate Cox models adjusted for age, T and N stage, grade, and progesterone receptor. Predictive value was assessed using histology-by-treatment interactions. Results: Among 5,748 pts in the ITT population, 4,982 (87%) were included (3,838 IBC-NST [67%], 1,144 ILC [20%]); median follow-up 6.9y. Compared with IBC-NST, ILC was associated with older age (median 54 vs 51 y), higher T stage (T3/T4: 41.7% vs 20.4%), fewer grade 3 tumors (12.7% vs 33.5%), higher mastectomy rates (74.5% vs 58.4%), less (neo)adjuvant chemotherapy (72.2% vs 86.2%), and less tamoxifen as initial ET (28.8% vs 34.5%) (all p<0.001). ILC prevalence varied by country: lower in Asia (Japan 10.5%, Korea 0%, Taiwan 2.8%) and higher in Europe (23.1%) and North America (24.0%). When evaluating the predictive value, palbo appeared to confer greater benefit in ILC for all endpoints (HRs ranging from 0.41 to 0.86) and not in IBC-NST (HRs ranging from 0.97 to 1.01), although the histology-by-treatment interaction was significant only for LRRFS (Table). In the overall population, 7-year IDFS was 79.3% for IBC-NST and 75.8% for ILC. While the difference was significant in univariable analysis (HR 1.17, 95% CI 1.01-1.35), it was not in multivariable analysis (HR 1.06, 0.91-1.24). Notably, the proportional hazards assumption was violated, and time-dependent modeling demonstrated that worse outcomes for ILC on IDFS, DRFS, and other endpoints emerged predominantly beyond 3 years. Conclusions: In this large, randomized dataset of pts with early HR+/HER2− breast cancer with long-term follow-up, ILC demonstrated distinct clinicopathologic features and geographic distribution. While ILC was not an independent prognostic factor over the entire follow-up, time-dependent modeling revealed worse long-term outcomes which only emerged after 3 years. Palbo appeared to be associated with more favorable outcomes in ILC than in IBC-NST across endpoints. These findings suggest a potential benefit of palbo in ILC that warrants further investigation in other adjuvant trials evaluating CDK4/6 inhibitors. Citation Format: G. Nader-Marta, C. Desmedt, D. Hlauschek, A. DeMichele, G. Zoppoli, E. Blondeaux, E. de Azambuja, M. Bellet-Ezquerra, O. Metzger-Filho, J. M. Suga, G. Pfeiler, M. P. Goetz, M. Ruiz-Borrego, S. Loibl, J. Meisel, A. Ring, K. Van Baelen, E. P. Mamounas, N. Zdenkowski, E. Agostinetto, M. Lambertini, E. Gauthier, L. Soelkner, A. C. Dueck, M. Gnant, E. L. Mayer. Long-term prognostic and predictive value of lobular histology in the PALLAS trial [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-11-06.

526 Background: The PALLAS trial (NCT02513394) investigated the efficacy of the addition of palbociclib (palbo) to standard adjuvant endocrine therapy (ET) to reduce breast cancer recurrence. Previous analyses of this trial have not shown significant benefit of combination palbo+ET over ET alone. Given prior data showing that extent of neutropenia is associated with response to palbo and other cell cycle-specific therapies, we evaluated whether extent of neutropenia could identify responders to palbo in the adjuvant setting. Methods: PALLAS is a global, open-label, phase III trial that randomized patients (pts) with stage II-III hormone-receptor positive, HER2-negative breast cancer to receive ET for ≥5 years with or without standard-dose palbo for 2 years in 28-day cycles. The primary endpoint is invasive disease-free survival (iDFS). For this exploratory analysis, the palbo population was classified into pts with treatment-emergent high-grade neutropenia (HGN) with maximum grade ≥3 (absolute neutrophil count <1000), or low-grade/no neutropenia (LGN) with maximum grade <2; these groups were compared to each other and to the ET alone group for 5-year iDFS outcomes. Logistic regression examined individual baseline characteristics associated with HGN during the first 3 cycles within the palbo group. Impact of HGN during the first 3, 6, and 12 cycles on iDFS was tested using univariate and multivariable landmark Cox regression. Results: The safety population included 5736 pts, 2840 allocated to palbo+ET, 2896 to ET alone. Prior publications reported no new safety signals, low rates of serious infection, and no grade 5 treatment-related events. The palbo+ET group consisted of 1006 (35.4%) LGN and 1834 (64.6%) HGN. 5-year iDFS results are shown in the table. Pts who received palbo+ET and developed HGN by the end of cycle 6 had significantly improved 5-year iDFS compared to those who received ET alone (p=0.04), which remained statistically significant when adjusting for body mass index (BMI), prior chemotherapy, and race. Multivariable logistic regression showed lower BMI, prior chemotherapy, Asian race, and prior mastectomy were significantly associated with HGN (all p<0.05). Conclusions: In this exploratory analysis of the phase III PALLAS adjuvant trial, addition of palbo to ET appeared to be superior to ET alone in pts who developed HGN in the first 6 cycles of treatment but not in those who had LGN. These findings are consistent with observations in the metastatic setting suggesting that neutropenia could be a useful biomarker for palbo concentration and efficacy. Clinical trial information: NCT02513394 . Maximum grade neutropenia measured at end of cycle: 5-year iDFS Palbo+ET HGN (%) Palbo+ET LGN (%) ET alone (%) Hazard Ratio p-value 3 84.9 84.4 1.06 0.54 84.9 82.9 1.17 0.06 6 85.6 84.9 1.08 0.44 85.6 83.4 1.19 0.04 12 86.3 85.9 1.06 0.57 86.3 85.0 1.12 0.20

ImportanceAdjuvant ovarian function suppression (OFS) with oral endocrine therapy improves outcomes for premenopausal patients with hormone receptor–positive (HR+) breast cancer but adds adverse effects. A genomic biomarker for selecting patients most likely to benefit from OFS-based treatment is lacking.ObjectiveTo assess the predictive and prognostic performance of the Breast Cancer Index (BCI) for OFS benefit in premenopausal women with HR+ breast cancer.Design, Setting, and ParticipantsThis prospective-retrospective translational study used all available tumor tissue samples from female patients from the Suppression of Ovarian Function Trial (SOFT). These individuals were randomized to receive 5 years of adjuvant tamoxifen alone, tamoxifen plus OFS, or exemestane plus OFS. BCI testing was performed blinded to clinical data and outcome. The a priori hypothesis was that BCI HOXB13/IL17BR ratio (BCI[H/I])–high tumors would benefit more from OFS and high BCI portended poorer prognosis in this population. Settings spanned multiple centers internationally. Participants included premenopausal female patients with HR+ early breast cancer with specimens in the International Breast Cancer Study Group tumor repository available for RNA extraction. Data were collected from December 2003 to April 2021 and were analyzed from May 2022 to October 2022.Main Outcomes and MeasuresPrimary end points were breast cancer–free interval (BCFI) for the predictive analysis and distant recurrence-free interval (DRFI) for the prognostic analyses.ResultsTumor specimens were available for 1718 of the 3047 female patients in the SOFT intention-to-treat population. The 1687 patients (98.2%) who had specimens that yielded sufficient RNA for BCI testing represented the parent trial population. The median (IQR) follow-up time was 12 (10.5-13.4) years, and 512 patients (30.3%) were younger than 40 years. Tumors were BCI(H/I)-low for 972 patients (57.6%) and BCI(H/I)-high for 715 patients (42.4%). Patients with tumors classified as BCI(H/I)-low exhibited a 12-year absolute benefit in BCFI of 11.6% from exemestane plus OFS (hazard ratio [HR], 0.48 [95% CI, 0.33-0.71]) and an absolute benefit of 7.3% from tamoxifen plus OFS (HR, 0.69 [95% CI, 0.48-0.97]) relative to tamoxifen alone. In contrast, patients with BCI(H/I)-high tumors did not benefit from either exemestane plus OFS (absolute benefit, −0.4%; HR, 1.03 [95% CI, 0.70-1.53]; P for interaction = .006) or tamoxifen plus OFS (absolute benefit, −1.2%; HR, 1.05 [95% CI, 0.72-1.54]; P for interaction = .11) compared with tamoxifen alone. BCI continuous index was significantly prognostic in the N0 subgroup for DRFI (n = 1110; P = .004), with 12-year DRFI of 95.9%, 90.8%, and 86.3% in BCI low-risk, intermediate-risk, and high-risk N0 cancers, respectively.Conclusions and RelevanceIn this prospective-retrospective translational study of patients enrolled in SOFT, BCI was confirmed as prognostic in premenopausal women with HR+ breast cancer. The benefit from OFS-containing adjuvant endocrine therapy was greater for patients with BCI(H/I)-low tumors than BCI(H/I)-high tumors. BCI(H/I)-low status may identify premenopausal patients who are likely to benefit from this more intensive endocrine therapy.

Abstract Background The PALLAS trial investigated the addition of palbociclib to standard adjuvant endocrine therapy reduces breast cancer recurrence. This pre-specified analysis was conducted to determine whether adjuvant palbociclib benefited patients diagnosed with lower risk stage IIA disease compared to those with higher stage disease. Methods PALLAS was an international, multicenter, randomized, open-label, phase III trial, representing a public-private partnership between Pfizer, the Austrian Breast Cancer Study Group and, the U.S. ALLIANCE Foundation. Patients diagnosed with stage II-III, hormone-receptor-positive, HER2/neu negative breast cancer who were within 12 months of diagnosis, and had completed all definitive therapy aside from endocrine therapy, which was started within 6 months prior to study entry. All patients were required to submit a formalin-fixed paraffin-embedded (FFPE) tumor block. Patients were randomly assigned 1:1 to receive standard adjuvant endocrine therapy (of physicians’ choice) for at least 5 years with or without 2 years of Palbociclib, administered orally at a starting dose of 125 mg daily, given for 21 days followed by a 7-day break. Results A total of 5,796 patients with HR+/HER2- early breast cancer (including 1,010 with stage IIA) were enrolled. Median follow-up was 50 months for stage IIA patients and 43.1 months overall. In the stage IIA cohort, four-year iDFS in the palbociclib arm was 92.9% versus 92.1% for ET alone (HR 0.75, 95%CI 0.48–1.19, p = 0.23). There was no differential benefit by histologic grade, chemotherapy receipt, age, or anatomic/clinical risk. Additionally, no benefit to palbociclib was seen in this cohort in invasive breast cancer-free survival (iBCFS), locoregional relapse-free survival (LRFS), distant relapse-free survival (DRFS), or overall survival (OS). For the stage IIB/III patients, 4-year iDFS was 85.3% for palbociclib + ET versus 83.6% for ET alone (HR 0.91, 95% CI 0.77–1.07, p = 0.24). Conclusions and Relevance: While there were substantial differences in outcome for stage IIA versus IIB/III patients at 4 years of follow-up, the addition of 2 years of palbociclib did not improve outcomes for patients, regardless of stage. Trial Registration: The study was registered on Clinicaltrials.gov on July 31, 2015, and was assigned the clinical trial number (NCT02513394).

PURPOSE BMI affects breast cancer risk and prognosis. In contrast to cytotoxic chemotherapy, CDK4/6 inhibitors are given at a fixed dose, irrespective of BMI or weight. This preplanned analysis of the global randomized PALLAS trial investigates the impact of BMI on the side-effect profile, treatment adherence, and efficacy of palbociclib. METHODS Patients were categorized at baseline according to WHO BMI categories. Neutropenia rates were assessed with univariable and multivariable logistic regression. Time to early discontinuation of palbociclib was analyzed with Fine and Gray competing risk models. Unstratified Cox models were used to investigate the association between BMI category and time to invasive disease-free survival (iDFS). 95% CIs were derived. RESULTS Of 5,698 patients included in this analysis, 68 (1.2%) were underweight, 2,082 (36.5%) normal weight, 1,818 (31.9%) overweight, and 1,730 (30.4%) obese at baseline. In the palbociclib arm, higher BMI was associated with a significant decrease in neutropenia (unadjusted odds ratio for 1-unit change, 0.93; 95% CI, 0.91 to 0.94; adjusted for age, race ethnicity, region, chemotherapy use, and Eastern Cooperative Oncology Group at baseline, 0.93; 95% CI, 0.92 to 0.95). This translated into a significant decrease in treatment discontinuation rate with higher BMI (adjusted hazard ratio [HR] for 10-unit change, 0.75; 95% CI, 0.67 to 0.83). There was no significant improvement in iDFS with the addition of palbociclib to ET in any weight category (normal weight HR, 0.84; 95% CI, 0.63 to 1.12; overweight HR, 1.10; 95% CI, 0.82 to 1.49; and obese HR, 0.95; 95% CI, 0.69 to 1.30) in this analysis early in follow-up (31 months). CONCLUSION This preplanned analysis of the PALLAS trial demonstrates a significant impact of BMI on side effects, dose reductions, early treatment discontinuation, and relative dose intensity. Additional long-term follow-up will further evaluate whether BMI ultimately affects outcome.

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported. The Suppression of Ovarian Function Trial (SOFT; ClinicalTrials.gov identifier: NCT00066690 ) randomly assigned premenopausal women with hormone receptor–positive breast cancer to 5 years of adjuvant tamoxifen, tamoxifen plus ovarian function suppression (OFS), or exemestane plus OFS. The primary analysis compared disease-free survival (DFS) between tamoxifen plus OFS versus tamoxifen alone; exemestane plus OFS versus tamoxifen was a secondary objective. After 8 years, SOFT reported a significant reduction in recurrence and improved overall survival (OS) with adjuvant tamoxifen plus OFS versus tamoxifen alone. Here, we report outcomes after median follow-up of 12 years. DFS remained significantly improved with tamoxifen plus OFS versus tamoxifen (hazard ratio, 0.82; 95% CI, 0.69 to 0.98) with a 12-year DFS of 71.9% with tamoxifen, 76.1% with tamoxifen plus OFS, and 79.0% with exemestane plus OFS. OS was improved with tamoxifen plus OFS versus tamoxifen (hazard ratio, 0.78; 95% CI, 0.60 to 1.01) and was 86.8% with tamoxifen, 89.0% with tamoxifen plus OFS, and 89.4% with exemestane plus OFS at 12 years. Among those who received prior chemotherapy for human epidermal growth factor receptor-2–negative tumors, OS was 78.8% with tamoxifen, 81.1% with tamoxifen plus OFS, and 84.4% with exemestane plus OFS. In conclusion, after 12 years, there remains a benefit from including OFS in adjuvant endocrine therapy, with an absolute improvement in OS more apparent with higher baseline risk of recurrence. [Media: see text]

PURPOSE Palbociclib is a cyclin-dependent kinase 4 and 6 inhibitor approved for advanced breast cancer. In the adjuvant setting, the potential value of adding palbociclib to endocrine therapy for hormone receptor–positive breast cancer has not been confirmed. PATIENTS AND METHODS In the prospective, randomized, phase III PALLAS trial, patients with hormone receptor–positive, human epidermal growth factor receptor 2–negative early breast cancer were randomly assigned to receive 2 years of palbociclib (125 mg orally once daily, days 1-21 of a 28-day cycle) with adjuvant endocrine therapy or adjuvant endocrine therapy alone (for at least 5 years). The primary end point of the study was invasive disease-free survival (iDFS); secondary end points were invasive breast cancer–free survival, distant recurrence-free survival, locoregional cancer-free survival, and overall survival. RESULTS Among 5,796 patients enrolled at 406 centers in 21 countries worldwide over 3 years, 5,761 were included in the intention-to-treat population. At the final protocol-defined analysis, at a median follow-up of 31 months, iDFS events occurred in 253 of 2,884 (8.8%) patients who received palbociclib plus endocrine therapy and in 263 of 2,877 (9.1%) patients who received endocrine therapy alone, with similar results between the two treatment groups (iDFS at 4 years: 84.2% v 84.5%; hazard ratio, 0.96; CI, 0.81 to 1.14; P = .65). No significant differences were observed for secondary time-to-event end points, and subgroup analyses did not show any differences by subgroup. There were no new safety signals for palbociclib in this trial. CONCLUSION At this final analysis of the PALLAS trial, the addition of adjuvant palbociclib to standard endocrine therapy did not improve outcomes over endocrine therapy alone in patients with early hormone receptor–positive breast cancer.