Citations

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).

Benign prostatic hyperplasia and prostate cancer are often associated with lower urinary tract symptoms, which can severely affect patient quality of life. To address this challenge, we developed and optimized an injectable compound, prostate ablation and drug delivery agent (PADA), for percutaneous prostate tissue ablation and concurrently delivered therapeutic agents. PADA is an ionic liquid composed of choline and geranic acid mixed with anticancer therapeutics and a contrast agent. The PADA formulation was optimized for mechanical properties compatible with hand injection, diffusion capability, cytotoxicity against prostate cells, and visibility of an x-ray contrast agent. PADA also exhibited antibacterial properties against highly resistant clinically isolated bacteria in vitro. Ultrasound-guided injection, dispersion of PADA in the tissue, and tissue ablation were tested ex vivo in healthy porcine, canine, and human prostates and in freshly resected human tumors. In vivo testing was conducted in a murine subcutaneous tumor model and in the canine prostate. In all models, PADA decreased the number of viable cells in the region of dispersion and supported the delivery of nivolumab throughout a portion of the tissue. In canine survival experiments, there were no adverse events and no impact on urination. The injection approach was easy to perform under ultrasound guidance and produced a localized effect with a favorable safety profile. These findings suggest that PADA is a promising therapeutic prostate ablation strategy to treat lower urinary tract symptoms.

e19057 Background: In ELM-2 (NCT03888105), a Ph 2, single arm, open label trial, odronextamab demonstrated robust efficacy, generally manageable safety, and overall maintenance of patient-reported outcomes (PROs) in R/R FL pts (Villasboas et al. ASH 2023). In FL, pts with disease progression within 2 yrs of frontline chemoimmunotherapy (POD24) are hard to treat with poor clinical outcomes, representing an unmet need. We report PROs by POD24 status in pts with Grade 1–3a R/R FL from ELM-2. Methods: Pts received IV odronextamab in 21-day cycles (C): 80 mg QW in C1–4, with C1 dose step up to mitigate cytokine release syndrome, then 160 mg Q2W (Q4W if complete response ≥9 mo) until progression. PROs were collected at baseline (BL), Wks 2–4, 10, then Q8W in Yr 1, and Q12W in Yr 2. Post-hoc POD24 subgroup analyses were performed on six EORTC QLQ-C30 scales, the EQ-5D-3L VAS, and FACT-Lym LymS. Estimated mean change from BL (CFB) was analyzed using mixed models for repeated measures (MMRM) through Wk 42 (≥10 pts at last assessment). Published meaningful CFB thresholds were used to define deterioration/improvement in responder analyses. Results: By Jan 31, 2023, 140 pts with R/R FL had received odronextamab. Pts with POD24 (n=70) were younger than pts without POD24 (n=70; median age 57.5 vs 62.0 y), had fewer prior Tx lines (median 2 vs 3), and a higher proportion double refractory to anti-CD20 Ab + alkylator (53% vs 29%). Objective response rate was similar in evaluable pts with (n=63; 79%) and without (n=65; 80%) POD24. PRO questionnaire completion ranged from 52–95% through Wk 42 across groups. Descriptive analyses suggest BL PRO scores were similar by POD24 status, showing good HRQoL/functioning and low symptom burden, and were generally maintained through Wk 42 with minimal between-group differences (overlapping 95% CIs for LS mean CFB [Table]). In both groups, more pts reported PRO maintenance or improvement vs deterioration across visits, except for fatigue at Wk 10 in pts without POD24. Conclusions: In pts with heavily pretreated R/R FL, odronextamab Tx maintained HRQoL, functioning, and symptoms irrespective of POD24 status. Clinical trial information: NCT03888105 . [Table: see text]

1037 Background: TBCRC041, a randomized phase 2 trial of alisertib (A) ± fulvestrant (F) in women with HR+/HER2- MBC demonstrated promising clinical activity for alisertib (1). Interrogation of baseline (PreC1) and end of cycle 1 (EOC1) cfDNA and CTCs may identify biomarkers associated with response to A±F. Methods: Plasma cfDNA was sequenced using the Guardant INFINITY platform, which includes genomic and methylated tumor fraction (mTF) analysis. Pathogenic variants were determined using publicly available databases and Mayo Clinic annotation pipelines. CTCs were identified as nucleated, EpCAM+/ cytokeratin+/ CD45- cells and assessed for ER/HER2 staining (RareCyte, Seattle). PFS was defined as the time from randomization to progression or death. EOC1-PFS differs from PFS as time starts at C2D1. Stratified log-rank tests and conditional Cox modeling were used to assess whether PFS or EOC1-PFS differed by mutations in ESR1 or PIK3CA, pre-CTC ≥ 5, or mTF>1%. Results: Of the 91 eligible pts, 84 progressed, and 73 were deceased. In the 86 pts with PreC1-cfDNA results, variants were identified in ESR1 (42; 48.8%), PIK3CA (36; 41.9%), AKT1 (7; 8.1%), PTEN(7; 8.1%), BRCA1 (4; 4.7%), and BRCA2 (7; 8.1%). Pts with a PIK3CAmut had significantly decreased PFS (HR 1.8; 95%CI: 1.1 -2.9, p=0.014) but not by ESR1mut status (p=0.583). PreC1 and EOC1-mTF were determined for 78 and 76 pts, respectively. PreC1-mTF was 0-1% in 21; 1.1-10.0% in 27; and 10.1-100% in 30. mTF levels remained between 0-1% in 17 pts fell to 0-1% in 11 pts, and was 0-1% in 5 pts without a preC1-mTF determination. PFS did not differ with respect to PreC1-mTF (p=0.210), but EOC1-PFS was worse in pts with mTF >1% (HR 3.0; 95%CI: 1.6 -5.2, p<0.001). PreC1 and EOC1-CTC were determined for 78 and 76 pts. 36 (46.2%) pts had a PreC1 CTC count ≥ 5. EOC1-CTC levels remained at (n=17) or increased to (n=1) ≥ 5 and was ≥ 5 in 2 pts without a preC1-CTC determination. EOC1-PFS was not significantly different for EOC1-CTC ≥ 5 (p=0.065), but was significantly decreased in pts with PreC1-CTC≥5 (HR=1.8; 95%CI: 1.1-3.0; p=0.018). Broader cfDNA NGS panel and CTC-derived ER/HER2 staining results will be presented at the meeting. Conclusions: Among patients receiving A±F, PFS varied based on the PIK3CAmutation status. cfDNA and CTC assessment PreC1 and EOC1 provided complementary information. Further validation in larger datasets is needed. 1. JAMA Oncol 2023;9:815. Clinical trial information: NCT02860000 .

538 Background: The phase 3 PALLAS trial compared 2 years of the CDK4/6 inhibitor palbociclib with endocrine therapy of provider choice, versus endocrine therapy alone, as adjuvant treatment for patients (pts) with Stage II-III hormone receptor-positive HER2-negative (HR+/HER2-) breast cancer. The SET2,3 index adjusts the measurement of SETER/PR index of endocrine receptor-related transcriptional activity with a baseline prognostic index (BPI) derived from tumor size (T), number of involved lymph nodes (N) and gene expression levels of ESR1, PGR, ERBB2 and AURKA (RNA4 subtype score). High SET2,3 (index ≥ 2.10) represents high endocrine sensitivity with favorable prognosis. Clinical outcome results from PALLAS were previously published, and the trial now has 5-year median follow-up. Methods: Participants in PALLAS provided a tumor tissue block prior to randomization. RNA was extracted from samples with sufficient tumor tissue and cellularity (>25mm2 with ≥20% cancer nuclei). SET2,3 index was measured from 300ng total RNA using the QuantiGene Plex platform (ThermoFisher, Waltham, MA) following the manufacturer’s protocol and using pre-defined quality control (QC) parameters and cut point. Results from primary tumor samples prior to systemic therapy were analyzed. Invasive disease-free survival (iDFS) was summarized with Kaplan-Meier plots using log-rank test. Cox models were adjusted for treatment arm assignment, with a treatment arm by SET index value interaction term to test for prediction of palbociclib benefit. The pre-defined level of significance was a two-sided 0.05. Results: There were 4075 pts from the total PALLAS population (N=5796) who provided a primary tumor sample that met pre-analytical requirements to perform the SET assay, from which 3388 (83%) results passed quality control, including 3093 from a sample obtained prior to receiving systemic therapy (1559 in palbociclib arm and 1534 in the control arm). SET2,3 index could not be calculated for 12 pts due to missing tumor or nodal information. There was no evidence of an interaction between treatment arm and SET indices (continuous) for iDFS: SET2,3 index interaction p=0.12 and SETER/PR index interaction p=0.92. Estimated 5-year iDFS was superior for those with high SET2,3: iDFS was 91.4% (95%CI 89.9–92.8) in 1719 (55.8%) pts with high SET2,3, versus 78.5% (95%CI 76.0–80.8) in 1362 (44.2%) pts with low SET2,3 (HR 0.38, 95%CI 0.31–0.47, p<0.0001). The SETER/PR index was also significantly associated with iDFS (HR 0.70 per 0.5 units, 95%CI 0.65–0.77, p<0.0001). Conclusions: There was no evidence that the SET2,3 or SETER/PR index of endocrine-related transcriptional activity predicts benefit from palbociclib treatment. SET2,3 index was strongly prognostic for pts with Stage II-III breast cancer, with excellent 5-year IDFS for pts classified as SET2,3 high. Clinical trial information: NCT02513394 .

Abstract Background The US Centers for Disease Control and Prevention recommends HIV testing every 3 months in oral PrEP users. We performed a national assessment of HIV testing compliance among oral PrEP users. Methods We analyzed 408 910 PrEP prescriptions issued to 39 809 PrEP users using a national insurance claims database that contained commercial and Medicaid claims. We identified PrEP use based on pharmacy claims and outpatient diagnostic coding. We evaluated the percentage of PrEP prescription refills without HIV testing (identified by CPT codes) within the prior 3, 6, and 12 months using time to event methods. We performed subgroup and multivariate analyses by age, gender, race, insurance type, and geography. Results Of 39 809 persons, 36 197 were commercially insured, 3612 were Medicaid-insured, and 96% identified as male; the median age (interquartile range) was 34 (29–44) years, and the Medicaid-insured PrEP users were 24% Black/African American, 44% White, and 9% Hispanic/Latinx. Within the prior 3, 6, and 12 months, respectively, the percentage of PrEP prescription fills in individuals without HIV Ag/Ab testing was 34.3% (95% CI, 34.2%–34.5%), 23.8% (95% CI, 23.7%–23.9%), and 16.6% (95% CI, 16.4%–16.7%), and the percentage without any type of HIV test was 25.8% (95% CI, 25.6%–25.9%), 14.6% (95% CI, 14.5%–14.7%), and 7.8% (95% CI, 7.7%–7.9%). Conclusions Approximately 1 in 3 oral PrEP prescriptions were filled in persons who had not received an HIV Ag/Ab test within the prior 3 months, with evidence of health disparities. These findings inform clinical PrEP monitoring efforts and compliance with national HIV testing guidance to monitor PrEP users.

Abstract Introduction: LAS is a selective estrogen receptor modulator (SERM)/tissue-selective estrogen agonist/antagonist studied in women with osteoporosis and vulvar-vaginal atrophy, and most recently, metastatic breast cancer (mBC) with ESR1 mutations. LAS data in healthy postmenopausal women and young men show linear PK and no differences by age or race (Gardner. J Clin Pharmacol 2006;46:52-58; Prakash. Drug Metab Dispos 2008;26:1218-26; Data on file). Also, no PK differences were found between Caucasian and Japanese patients (Jhee. AACR-JCA 2022, abstract A83; Fountaine. J Clin Pharmacol 2006;46:693-99). Here we report select PK data of LAS (5 mg/day) from women with mBC in the ELAINE 1 and ELAINE 2 oncology trials to indirectly investigate possible drug-drug interactions between LAS and Abema. Methods: Patients with mBC and ESR1 mutations who progressed on endocrine therapy and CDK4/6 inhibitors received LAS 5 mg/day as monotherapy (ELAINE 1) or combined with Abema (provided by Eli Lilly and Co) 150 mg BID (ELAINE 2). Blood was collected prior to daily dosing at weeks 2, 4, 8, and every 4 weeks up to the final visit in ELAINE 1, and visits during the first 8 weeks in ELAINE 2, to determine the plasma trough steady-state concentrations (Css) of LAS, Abema, and two active Abema metabolites (M2 and M20). LAS was assayed using validated high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS; detection 0.025 to 25.0 ng/mL); levels below the lower limit of quantification (LLOQ) were reported as 0 ng/mL. Abema and its M2 and M20 metabolites were measured by validated Turbo Ion Spray LC/MS/MS (detection 1.00 to 500 ng/mL); values below the LLOQ were reported as &lt; LLOQ ng/mL. Mean trough Css at each visit were calculated for LAS (ELAINE 1 and 2), and Abema and its M2 and M20 metabolites (ELAINE 2). LAS levels from ELAINE 1 and 2 were compared, while Abema, M2 and M20 plasma levels in ELAINE 2 were compared with previously reported levels. Such indirect comparisons may help determine if Abema altered the metabolism of LAS, or if LAS altered that of Abema, M2, or M20. The relationships of LAS and Abema levels with progression-free survival (PFS) were also explored. Results: Across all time points for subjects who had PK samples assessed, the LAS mean trough Css was 33.6 ng/mL (CV%, 39.8) in ELAINE 1 (n=40) and 30.9 ng/mL (CV 50.5%) in ELAINE 2 (n=29); in both studies, LAS concentrations were consistent across visits. LAS levels in ELAINE 2 were similar to those in ELAINE 1 with no evidence of accumulation. Mean (CV%) Abema plasma concentrations at weeks 2, 4, 6 and 8 were 199 (102%), 107 (130%), 82 (271%), and 94.3 (223%) ng/mL, respectively. Minimum and maximums of the mean trough Css for LAS, Abema, M2, and M20 are shown in Table 1. No relationships between LAS or Abema levels and antitumor activity measured by PFS were seen (data to be presented). Conclusion: The steady-state PK of 5 mg LAS in the ELAINE 1 and 2 studies suggest that the addition of abemaciclib to LAS did not result in an obvious or significant LAS-Abema, drug-drug interaction. Abema PK data from ELAINE 2 were consistent with published data (European Medicines Agency, Verzenio). These results support the continued development of LAS alone and combined with Abema for treating ER+/HER2-, ESR1-mutated mBC that progressed on endocrine therapy and CDK4/6 inhibitors. Table. Mean trough, steady-state concentrations of lasofoxifene and abemaciclib. XX- XX aData from patients who received oral LAS (5 mg/day) plus Abema (150 mg BID). Abema, abemaciclib; LAS, lasofoxifene; M2 and M20 are Abema metabolites. Citation Format: Senthil Damodaran, Paul V. Plourde, Simon Jenkins, Phil Mayer, David J Portman, Matthew Goetz. Pharmacokinetics (PK) of lasofoxifene (LAS) monotherapy and combined with abemaciclib (Abema) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-05.

Abstract Introduction: Analyses of multiple clinical trials have suggested racial and ethnic disparities in outcomes for early-stage, hormone receptor-positive and HER2-negative (HR+HER2-) breast cancer, however, none of these studies examined the use of adjuvant CDK4/6 inhibitors. The objective of this study was to explore racial and ethnic differences in toxicity, treatment duration, and disease outcomes in patients (pts) with early-stage HR+HER2- breast cancer treated with or without adjuvant palbociclib on the PALLAS trial. Methods: The PALLAS phase III, global, open-label trial randomized 5,796 pts with stage II-III HR+HER2- breast cancer to 2 years of palbociclib plus ongoing provider/patient choice adjuvant endocrine therapy (ET+palbo) vs. ET alone (ET). The analytic cohort was limited to pts enrolled in North America with known self-reported race and ethnicity (Non-Hispanic White, Non-Hispanic Black, Hispanic, Asian or Pacific Islander). Descriptive statistics were used to examine treatment characteristics, early discontinuation, and toxicity by race and ethnicity. Kaplan-Meier curves were used to estimate 3-year locoregional recurrence-free survival (LRFS) and invasive disease-free survival (IDFS) stratified by racial and ethnic group. Cox proportional hazards models were used identify predictors of LRFS and IDFS. Results: 2,547 North American pts were randomized and included in the intent-to-treat population with a median follow-up of 59.8 months; 1,996 (78.4%) identified as Non-Hispanic White (NHW), 132 (5.2%) Non-Hispanic Black (NHB), 156 (6.1%) Hispanic, and 134 (5.3%) Asian or Pacific Islander (API). Stage, performance status, type of surgery, and prior radiation were similar across racial and ethnic groups. Age, body mass index, grade, and prior chemotherapy differed by race and ethnicity (p&lt; 0.05). Median age was lowest in API pts and highest in NHW pts (47.5 vs 53.0 years, respectively). Median body mass index was lowest in API and highest in NHB pts (24.4 vs 30.9). NHB pts were most likely to have high-grade disease (40.9% vs 26.9-30.5% in other groups). NHW pts were least likely to have received prior chemotherapy (81.0% vs 87.1-91.0%). Palbociclib early discontinuation was lowest in NHB pts (50.7%) and highest in Hispanic pts (65.9%), p=0.14. ET early discontinuation was similar across all groups (p=0.35). Palbociclib grade 3-4 overall toxicity was variable across groups (NHW 71.6%, NHB 79.1%, Hispanic 69.5%, API 85.2%), but this variation did not reach statistical significance (p=0.07). Neutropenia was highest in API pts (90.0% vs 57.3% in NHW, 58.2% in NHB, and 51.2% in Hispanic pts, p&lt; 0.01). Overall 3-year LRFS was 98% (95% CI 97-98%) and IDFS was 89% (95% CI 88-90%). LRFS and IDFS were statistically similar by race and ethnicity and within each study arm (Table). No differences in LRFS or IDFS were seen by race or ethnicity in adjusted models (p=0.95). Conclusions: In this clinical trial population of HR+HER2- breast cancer patients exposed to similar treatments, no racial/ethnic differences were seen in short-term LRFS or IDFS across study arms. Differences in palbociclib toxicity by racial and ethnic group, particularly neutropenia, were seen with the highest toxicity in API patients; however, this difference did not translate into early discontinuation of palbociclib or ET. Table: 3-year Kaplan-Meier Survival Outcomes Stratified by Race and Ethnicity Citation Format: Olga Kantor, Oluwadamilola (Lola) Fayanju, Amylou Dueck, Michael Gnant, Harold Burstein, Matthew Goetz, Claudine Isaacs, Lois Shepherd, Olwen Hahn, Daniel Anderson, Kathy Miller, Hope Rugo, Tiffany Traina, Zoneddy Dayao, Katherine Clifton, Eric Winer, Antonio Wolff, Norman Wolmark, Dongrui Lu, Patrick O'Brien, Sara Scovil, Angela DeMichele, Erica Mayer. Racial and Ethnic Differences in Clinical Outcomes among North American Patients with Hormone Receptor-Positive, HER2-negative, Early Breast Cancer in the PALLAS Trial (AFT-05) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-02-05.

Abstract Background: Low levels of HER2 expression (HER2-low) have recently emerged as a therapeutic target in patients (pts) with breast cancer (BC). The aim of this study was to evaluate clinical and demographic variables associated with HER2 expression, as well as the value of HER2-low as a prognostic and predictive biomarker for palbociclib benefit in pts enrolled in the PALLAS trial. Methods: The phase III PALLAS trial investigated the addition of palbociclib to adjuvant endocrine therapy (ET) in pts with stage II-III hormone receptor-positive BC. The aims of this analysis are (1) to assess the association between the presence of low levels of HER2 expression with demographic and clinicopathological parameters, (2) to test the prognostic value of HER2-low status on invasive disease-free survival (IDFS), distant relapse-free survival (DRFS), and overall survival (OS) and (3) to assess the value of HER2 expression as a predictive biomarker of response to palbociclib. HER2-low was defined as HER2 immunohistochemistry (IHC) 1+ or IHC 2+ with negative in situ hybridization; all pathologic evaluation was performed locally. Pts with HER2-0 and Her2-low BC were included in this analysis; those with HER2-positive BC or missing HER2 status were excluded. Association of HER2 with other baseline covariates were tested with Chi-squared tests. Prognostic and predictive power of HER2 were assessed with Cox Models. Multivariable models included age, T-stage, N-stage, grade and progesterone receptor (PR) expression. Hazard ratios (HR) and 95% Confidence intervals (CI) are reported. Results: From the original PALLAS intention-to-treat population (N = 5,753), 5304 pts (92.2%) were included in this analysis. Among these, 2,254 pts (42.5%) were classified as HER2 IHC 0 (HER2-0) and 3,050 (57.5%) as HER2-low (1,838 with IHC 1+ and 1,212 with IHC 2+). For this analysis, median follow-up was 59.8 months. Compared to HER2-0, pts with HER2-low tumors had statistically higher estrogen receptor expression levels (mean expression 89.2% vs 88.2%, p = 0.019), lower PR expression levels (65.9% vs 68.2%, p = 0.007). Importantly, HER2-low status varied significantly across 21 participating countries (range 16.7% to 75.6%; p&lt; 0.001) and was more frequent in pts enrolled in North America (63.1%) than in Europe (53.4%) and other regions (53.4%) (p &lt; 0.001). No differences in HER2 expression were observed according to anatomic stage, T-stage, N-stage, histological grade, age, menopausal status, primary surgery type, prior radiation, prior chemotherapy, or baseline performance status. There were no statistically significant differences in IDFS, DRFS or OS according to HER2 status in univariate or multivariable Cox models (prognostic value, HR provided in the Table). There was no significant interaction between the HER2 status and the benefit to palbociclib in IDFS, DRFS or OS (Table). Similar results were obtained when HER2-0 was compared to HER2 1+ and HER2 2+ separately. Conclusions: In this large, prospective and international cohort, no differences were observed in clinical parameters, prognosis, or differential benefit from palbociclib (predictive value) between HER2-0 and HER2-low tumors. Significant geographic variability was observed in the prevalence of HER2-low status, suggesting a high degree of variation in pathologic assessment of HER2 expression without impact on outcomes. Support: AFT, Abbvie Pfizer; Clinicaltrials.gov: NCT02513394 https://acknowledgments.alliancefound.org Citation Format: Guilherme Nader-Marta, Christian F. Singer, Dominik Hlauschek, Angela DeMichele, Paolo Tarantino, Georg Pfeiler, Miguel Martín, Justin Balko, Zbigniew Nowecki, Marija Balic, Adam Brufsky, Arlene Chan, Patrick G. Morris, Tufia Haddad, Sibylle Loibl, Yuan Liu, Lidija Sölkner, Christian Fesl, Erica Mayer, Michael Gnant. Clinical characterization, prognostic and predictive values of HER2-low in early breast cancer in the PALLAS trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-13.

Abstract Background. The phase 3 PALLAS trial (NCT02513394) compared two years of the CDK4/6 inhibitor palbociclib with endocrine therapy of provider choice, versus endocrine therapy alone, as adjuvant treatment for patients with Stage II-III hormone receptor-positive HER2-negative (HR+/HER2-) breast cancer. Genomic subtype (PAM50 intrinsic subtype) measured from whole-transcriptome RNA sequencing data was defined in the protocol of the PALLAS trial as the primary biomarker for analysis of prediction and prognosis. Clinical data have been previously presented (Gnant et al, JCO 2022), and the trial now has 5-year median follow-up. Methods. As part of trial eligibility, all participants in PALLAS provided a tumor tissue block prior to randomization (surgical if primary resection, core biopsy if neoadjuvant treatment) for translational analyses (TRANS-PALLAS). The biorepository and laboratory were blinded to identity and processed samples in random order, to minimize bias. Nucleic acids were extracted from samples with sufficient tumor tissue and cellularity (&gt;25 mm2 with ≥20% cancer nuclei). The Genome Sequencing Center at Washington University St. Louis performed whole-transcriptome RNA sequencing. Libraries were prepared from 1 µg DNase-1 treated total RNA, if total RNA DV200 &gt;28 (Agilent Bioanalyzer), using an unbiased library protocol of RNA HyperPrep kit with RiboErase (HMR) (Kapa Biosystems, Wilmington, MA). 100 bp paired-end sequencing was performed on NovaSeq 6000 using S4 Reagent Kit (Illumina, San Diego, CA), with 48 libraries pooled per lane. Intrinsic subtype was determined using Bioclassifier package (Research PAM50 script, Parker et al.) only for the analysis population of primary breast cancer samples that had not been exposed to prior neoadjuvant therapy. Invasive disease-free survival (IDFS) will be visualized using Kaplan-Meier plots, with log-rank test between groups. Cox models of proportional hazards will be developed to evaluate prognosis adjusted for known clinical covariates, or for predictive interactions. The pre-defined level of significance is a two-sided 0.05. Results. From the total study population of 5796 enrolled patients, 4655 tissue blocks had sufficient tumor content to process for RNA, with 3931 yielding sufficient RNA for sequencing, and 2669/4655 (57.3%) submitted tissue blocks had DV200 ≥28 and were successfully sequenced. Clinical unblinding revealed 2370 unique patients (1182 in the palbociclib treatment arm and 1188 in the control arm) with intrinsic subtype defined from their untreated primary tumor: 1555 (65.6%) luminal A, 287 (12.1%) luminal B, 167 (7.0%) HER2-enriched, 310 (13.1%) basal-like, 51 (2.2%) normal-like. We will report the results for association of molecular subtype, proliferation score, and Risk of Recurrence (ROR) scores with invasive disease-free survival (IDFS) by treatment arm at the meeting. Conclusions. The TRANS-PALLAS cohort represents one of the largest biorepositories of HR+/HER2- early breast cancer reflecting contemporary systemic management in the framework of a prospectively randomized global trial. Required tumor block submission in this phase 3 trial yielded data from unbiased whole-transcriptome RNA sequencing of the primary tumor prior to treatment from 41% of the PALLAS participants. The proportion of luminal A cancers was unexpectedly high (66%), indicating a lower-risk distribution of cancers in this population. The planned analyses of prediction and prognosis are ongoing and those results will be presented at the time of the meeting. Support: AFT, ABCSG, Pfizer, ECOG-ACRIN, NSABP Foundation, GBG, BIG; Clinicaltrials.gov Identifier: NCT02513394; https://acknowledgments.alliancefound.org Citation Format: Daniel Stover, Dominik Hlauschek, Erica Mayer, W. Fraser Symmans, Mark Watson, Iros Barozzi, Martin Filipits, Karla Ballman, Meritxell Bellet- Ezquerra, Justin Balko, Gabor Rubovszky, Nicholas Zdenkowski, Adam Brufsky, Guenther Steger, Claudine Isaacs, Sibylle Loibl, Fernando Henao, Meredith Regan, Yuan Liu, Christian Fesl, Patrick O'Brien, Angela DeMichele, Michael Gnant, Otto Metzger. Protocol-defined biomarker analysis in the PALLAS (AFT-05) adjuvant trial: Genomic subtype derived from RNA sequencing of HR+/HER2- early breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS03-07.