Neoadjuvant palbociclib plus either giredestrant or anastrozole in oestrogen receptor-positive, HER2-negative, early breast cancer (coopERA Breast Cancer): an open-label, randomised, controlled, phase 2 study

BACKGROUND

The development of more potent selective oestrogen receptor antagonists and degraders (SERDs) that can be orally administered could help to address the limitations of current endocrine therapies. We report the primary and final analyses of the coopERA Breast Cancer study, designed to test whether giredestrant, a highly potent, non-steroidal, oral SERD, would show a stronger anti-proliferative effect than anastrozole after 2 weeks for oestrogen receptor-positive, HER2-negative, untreated early breast cancer.

METHODS

In this open-label, randomised, controlled, phase 2 study, postmenopausal women were eligible if they were aged 18 years or older; had clinical T stage (cT)1c to cT4a-c (≥1·5 cm within cT1c) oestrogen receptor-positive, HER2-negative, untreated early breast cancer; an Eastern Cooperative Oncology Group performance status of 0-1; and baseline Ki67 score of at least 5%. The study was conducted at 59 hospital or clinic sites in 11 countries globally. Participants were randomly assigned (1:1) to giredestrant 30 mg oral daily or anastrozole 1 mg oral daily on days 1-14 (window-of-opportunity phase) via an interactive web-based system with permuted-block randomisation with block size of four. Randomisation was stratified by cT stage, baseline Ki67 score, and progesterone receptor status. A 16-week neoadjuvant phase comprised the same regimen plus palbociclib 125 mg oral daily on days 1-21 of a 28-day cycle, for four cycles. The primary endpoint was geometric mean relative Ki67 score change from baseline to week 2 in patients with complete central Ki67 scores at baseline and week 2 (window-of-opportunity phase). Safety was assessed in all patients who received at least one dose of study drug. The study is registered with ClinicalTrials.gov (NCT04436744) and is complete.

FINDINGS

Between Sept 4, 2020, and June 22, 2021, 221 patients were enrolled and randomly assigned to the giredestrant plus palbociclib group (n=112; median age 62·0 years [IQR 57·0-68·5]) or anastrozole plus palbociclib group (n=109; median age 62·0 [57·0-67·0] years). 15 (7%) of 221 patients were Asian, three (1%) were Black or African American, 194 (88%) were White, and nine (4%) were unknown races. At data cutoff for the primary analysis (July 19, 2021), the geometric mean relative reduction of Ki67 from baseline to week 2 was -75% (95% CI -80 to -70) with giredestrant and -67% (-73 to -59) with anastrozole (p=0·043), meeting the primary endpoint. At the final analysis (data cutoff Nov 24, 2021), the most common grade 3-4 adverse events were neutropenia (29 [26%] of 112 in the giredestrant plus palbociclib group vs 29 [27%] of 109 in the anastrozole plus palbociclib group) and decreased neutrophil count (17 [15%] vs 16 [15%]). Serious adverse events occurred in five (4%) patients in the giredestrant plus palbociclib group and in two (2%) patients in the anastrozole plus palbociclib group. There were no treatment-related deaths. One patient died due to an adverse event in the giredestrant plus palbociclib group (myocardial infarction).

INTERPRETATION

Giredestrant offers encouraging anti-proliferative and anti-tumour activity and was well tolerated, both as a single agent and in combination with palbociclib. Results justify further investigation in ongoing trials.

FUNDING

F Hoffmann-La Roche.

Next-Generation Estrogen Receptor–Targeted Therapeutics

Estrogen receptor (ER) α is expressed in the vast majority of breast cancers and is one of the most successfully prosecuted drug targets in oncology, with multiple classes of endocrine therapies approved for the treatment of ER+ breast cancer. These existing agents are highly active, both as single agents and as combination partners for other targeted therapies, and have significantly benefited patients. However, each of these standard-of-care (SOC) therapies has liabilities that allow for the reengagement of ER signaling as a mechanism of resistance. Data supporting the continued dependence of tumors on ER signaling following exposure to SOC agents have underpinned an extraordinary reenergizing of academic, biotechnology, and pharmaceutical groups pursuing next-generation ER-targeted therapies. The hypothesis that there remains an opportunity to bring further meaningful benefit to patients through fully optimized ER-targeted therapies is currently being investigated in the clinic.

Expected final online publication date for the Annual Review of Cancer Biology, Volume 7 is April 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Abstract P6-04-09: Variations in diagnostic practice of Ki67 scoring suggest standard guidelines needed for pathological assessment: survey results of global Ki67 testing methods

BACKGROUND The cell proliferation biomarker Ki67 is expressed during every phase of the cell cycle and has long been used as a diagnostic tool for cancer prognosis, especially for hormone receptor positive breast cancer (HR+ BC). More recently, Ki67 has emerged as a companion diagnostic to select patients for the medicines targeting high risk HR+ BC. We report survey results of local Ki67 immunohistochemistry (IHC) testing practices across 99 pathology labs in 11 countries supporting clinical trial sites in 2020-2021 for the coopERA Breast Cancer clinical study in neoadjuvant HR+ BC (NCT04436744). METHODS The survey was disseminated to pathology labs across five continents to assess local Ki67 IHC staining, analysis, and scoring methodologies. Metrics included pre-analytical considerations (e.g. sample type and requirements) and analytical considerations (e.g. test validation status, antibody, scoring methods, reporting). RESULTS All pathology labs reported requiring formalin-fixed, paraffin-embedded (FFPE) tissue for local Ki67 testing with 89% using sections with thickness of 2-5 microns. For the Ki67 test, the majority (65%) reported using an in vitro diagnostic assay, 23% used a validated test, and 8% utilized a research-use-only assay. Ki67 antibody selection varied among the labs with 46% using the MIB-1 mouse monoclonal (Dako Agilent), followed by 33% using the 30-9 rabbit monoclonal (Ventana) and 12% reporting the SP6 rabbit monoclonal (Thermo Fisher). A majority (65%) reported using single pathologist visual assessment for scoring, and 17% reported using two or more pathologists. Use of automated digital image analysis (ADIA) was reported by 18% of labs, either alone or in combination with pathologist visual assessment. A significant portion (75%) reported using the International Ki67 in Breast Cancer Working Group (IKWG) recommendations, whereas 7% reported using only digital image analysis (e.g. Ventana Virtuoso). A minority (7%) indicated neither and instead described variations of “eyeball” or “hot spot” visual estimates. Most labs (65%) reported counting at least 500 cells with 15% of these counting more than 1000 cells. Remaining labs (30%) counted less than 500 or no cells. Predominantly, 85% reported counting cells in at least 3 or more high power fields. Most labs (96%) report Ki67 scores as a percentage of positive nuclei and the remaining minority reported using other methods (e.g. ranges [< 10%, 10-20%, etc.] or H-score [0-300]). CONCLUSIONS The survey results suggest high global variability of local Ki67 testing practices with the highest variability observed in the test validation status, Ki67 clone, and scoring methods. Despite efforts by the IKWG to harmonize and increase the clinical validity of Ki67 as a biomarker, many labs indicating IKWG compliance had survey answers that were discordant with the specific guidelines set forth by the working group. Taking into account the totality of all answers provided by each respondent, only 51% of the surveyed labs fully conformed to the IKWG recommendations. Moreover, a small fraction conducts global estimations without specific cell counting or use “hot spot” scoring methods, despite the high variability and low reproducibility of these scores both intra- and inter-lab. This study demonstrates the benefits of using a central assay in clinical studies to reduce the variability of local Ki67 results in identifying high risk HR+ BC patients and suggests more work is needed to streamline the analytical practices of local Ki67 methodologies, which may directly impact clinical decisions such as the use of neoadjuvant therapies in HR+ BC.

Citation Format: Heather M. Moore, Wendy W. Lin, Tharu M. Fernando, Celine Lopez, Emma Kent, Karine Ellouk, Jennifer M. Giltnane. Variations in diagnostic practice of Ki67 scoring suggest standard guidelines needed for pathological assessment: survey results of global Ki67 testing methods [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-04-09.

VERONICA: Randomized Phase II Study of Fulvestrant and Venetoclax in ER-Positive Metastatic Breast Cancer Post-CDK4/6 Inhibitors - Efficacy, Safety, and Biomarker Results

PURPOSE

Despite promising activity in hematopoietic malignancies, efficacy of the B-cell lymphoma 2 (BCL2) inhibitor venetoclax in solid tumors is unknown. We report the prespecified VERONICA primary results, a randomized phase II clinical trial evaluating venetoclax and fulvestrant in estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer, post-cyclin-dependent kinase (CDK) 4/6 inhibitor progression.

PATIENTS AND METHODS

Pre-/postmenopausal females ≥18 years were randomized 1:1 to venetoclax (800 mg orally daily) plus fulvestrant (500 mg intramuscular; cycle 1: days 1 and 15; subsequent 28-day cycles: day 1) or fulvestrant alone. The primary endpoint was clinical benefit rate (CBR); secondary endpoints were progression-free survival (PFS), overall survival, and safety. Exploratory biomarker analyses included BCL2 and BCL extra-large (BCLXL) tumor expression, and PIK3CA circulating tumor DNA mutational status.

RESULTS

At primary analysis (cutoff: August 5, 2020; n = 103), venetoclax did not significantly improve CBR [venetoclax plus fulvestrant: 11.8% (n = 6/51; 95% confidence interval (CI), 4.44-23.87); fulvestrant: 13.7% (7/51; 5.70-26.26); risk difference -1.96% (95% CI, -16.86 to 12.94)]. Median PFS was 2.69 months (95% CI, 1.94-3.71) with venetoclax plus fulvestrant versus 1.94 months (1.84-3.55) with fulvestrant (stratified HR, 0.94; 95% CI, 0.61-1.45; P = 0.7853). Overall survival data were not mature. A nonsignificant improvement of CBR and PFS was observed in patients whose tumors had strong BCL2 expression (IHC 3+), a BCL2/BCLXL Histoscore ratio ≥1, or PIK3CA-wild-type status.

CONCLUSIONS

Our findings do not indicate clinical utility for venetoclax plus fulvestrant in endocrine therapy-resistant, CDK4/6 inhibitor-refractory metastatic breast tumors, but suggest possible increased dependence on BCLXL in this setting.

Neoadjuvant giredestrant (GDC-9545) plus palbociclib (P) versus anastrozole (A) plus P in postmenopausal women with estrogen receptor–positive, HER2-negative, untreated early breast cancer (ER+/HER2– eBC): Final analysis of the randomized, open-label, international phase 2 coopERA BC study

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Background: Endocrine therapy (ET) is the therapeutic mainstay for ER+ BC. Giredestrant is a highly potent, nonsteroidal, oral, selective ER antagonist and degrader (SERD) which has demonstrated robust ER occupancy, is well tolerated, and has previously shown encouraging antitumor activity as monotherapy and in combination with P in metastatic BC. coopERA BC (NCT04436744) evaluated giredestrant in eBC and met its primary endpoint, highlighting superior Ki67 suppression with single-agent giredestrant vs A at Week 2. Giredestrant was well tolerated. Here, we report the final analysis. Methods: Eligible patients (pts) with measurable ER+/HER2– untreated eBC and baseline Ki67 score ≥5% (202 planned) were randomized 1:1 to receive, on Days 1–14 of a neoadjuvant window-of-opportunity phase, 30 mg oral daily (PO QD) giredestrant or 1 mg PO QD A followed by a 16-week neoadjuvant phase of QD giredestrant or A for four 28-day cycles with 125 mg PO P on Days 1–21. Randomization was stratified by tumor size, baseline Ki67 score, and progesterone receptor status. Endpoints assessed here included Ki67 suppression from baseline to surgery, complete cell cycle arrest (CCCA; Ki67 ≤2.7%) at surgery, objective response rate (ORR), and safety. Results: At final analysis (cutoff: Nov 24, 2021), 112 and 109 pts were randomized to the giredestrant and A arms, respectively (median age: 62 years each; stage I/IIa disease: 60% vs 54%). Consistent with the primary analysis, greater suppression of Ki67 was observed at surgery with giredestrant + P (–81% [95% confidence interval (CI): –86%, –75%]) vs A + P (–74% [95% CI: –80%, –67%]). Similarly, greater CCCA was achieved at surgery with giredestrant + P (20%) vs A + P (14%). ORR was similar between the two arms (giredestrant + P: 50% [95% CI: 40%, 60%]; A + P: 49% [95% CI: 39%, 59%]). ET-related adverse events (AEs) were non-serious and occurred at similar rates between the two arms. Related Grade ≥3 AE rates were also similar at 6% each. Interruption/withdrawal of ET due to AEs was low and similar for both arms. Conclusions: In this final analysis of coopERA BC, the greater suppression of Ki67 with giredestrant vs A observed at Week 2 in the primary analysis was maintained at surgery, and safety data remained consistent with the known safety profile of giredestrant. coopERA BC is the first randomized study to show superior antiproliferative activity of an oral SERD (giredestrant) over an aromatase inhibitor (A) in ER+/HER2– eBC; studies are ongoing to further assess giredestrant’s clinical benefit. Clinical trial information: NCT04436744.

Abstract P5-13-06: Exploratory biomarker analysis in VERONICA, a phase 2 study of venetoclax + fulvestrant versus fulvestrant in patients with estrogen receptor (ER)-positive HER2-negative metastatic breast cancer (mBC)

BACKGROUND: Venetoclax (VEN) is a potent and selective inhibitor of the anti-apoptotic protein, BCL2. Preclinical studies have implicated the BCL2 family members, BCLXL and MCL1, in VEN resistance, and clinical studies in hematological malignancies have demonstrated subgroups with high ratios of BCL2/BCLXL and BCL2/MCL1 have the greatest VEN antitumor activity. The randomized phase 2 VERONICA study (NCT03584009) evaluated VEN in combination with fulvestrant (F) vs F alone in ER-positive, HER2-negative MBC pts who experienced disease recurrence/progression during or after a CDK4/6 inhibitor. Previously reported results from VERONICA (Lindeman et al. ASCO 2021) did not show an improved clinical benefit rate or progression-free survival (PFS) with VEN+F vs F alone. Here we present exploratory biomarker analyses of the expression of BCL2 family members and genomic alterations in circulating tumor DNA (ctDNA) and association with clinical outcomes from VEN+F vs F. METHODS: Tumor specimens were obtained during screening from 103 patients enrolled in the study, and expression levels of BCL2, BCLXL and MCL1 were analyzed by IHC. Baseline plasma-derived ctDNA was evaluated using the FoundationOne® Liquid assay. Expression of BCL2, BCLXL, MCL1 and mutations in ctDNA were correlated with PFS from VEN+F vs F based on the primary analysis (cutoff: Aug 5, 2020). RESULTS: In the overall population, protein levels of BCL2, BCLXL and MCL1 were similar between the VEN+F vs F arms. Patients whose tumors were BCL2 3+ trended towards having the greatest difference in median (m) PFS (3.9 months [mo] in VEN+F vs 1.7 mo in F; hazard ratio [HR] 0.38 [95% CI 0.09, 1.62]) albeit in a small sample size (n=13). Similarly, subgroup analysis suggested a trend for increasing mPFS and improved HR in VEN+F vs F alone in patients with the lowest BCLXL expression. mPFS in patients with a BCL2/BCLXL ratio ≥1 was 3.7 mo for VEN+F vs 1.8 mo for F (HR 0.67 [95% CI 0.3-1.49]) whereas patients with a BCL2/BCLXL ratio <1 had no difference in mPFS between the arms (2.0 mo in both arms, HR 1.21 [95% CI 0.7-2.1]). In the ctDNA-evaluable population, ESR1 (42.6%), TP53 (41.5%) and PIK3CA (35%) were the most prevalent genomic alterations observed and well-controlled between arms. PFS was similar between the ESR1 wildtype (wt) and mutant (mut) subgroups. TP53 mut status was a poor prognostic factor in both treatment arms. The PIK3CA wt subgroup had increased mPFS with VEN+F vs F alone (HR 0.66 [95% 0.38-1.17]) compared to PIK3CA mut (HR 1.59 [95% 0.74-3.34]). Patients with PIK3CA wt and BCL2 high tumors had the largest difference in mPFS between VEN+F (3.7 mo) vs F alone (1.9 mo) (HR 0.58 [95%CI 0.28-1.19]), compared to PIK3CA wt-BCL2 low tumors (2.4 vs 1.9 mo; HR 0.67 [95%CI 0.26-1.72]). CONCLUSION: Our data suggest that a high ratio of BCL2 to BCLXL conferred a trend towards a greater benefit to VEN+F compared to F alone, consistent with other clinical studies evaluating VEN. These analyses highlight the need to profile BCL2 and its family members to identify the VEN-sensitive subgroups, especially in indications where high expression of BCLXL or MCL1 may be observed. The ctDNA profile of VERONICA patients indicate a heavily pretreated patient population. The benefit observed in PIK3CA wt patients from VEN+F suggest increased dependence on BCL2 in this subgroup, while PIK3CA mut tumors likely rely on PI3K/AKT/mTOR survival programs or other BCL2 family members to evade apoptosis. Exploratory biomarker analyses are ongoing to further understand the VERONICA patient population.

Citation Format: Geoffrey J. Lindeman, Tharu M. Fernando, Rebecca Bowen, Ching-Wei Chang, Rupal Desai, Kushagra Gupta, Aulde Fléchais, Timothy R. Wilson, Aditya Bardia. Exploratory biomarker analysis in VERONICA, a phase 2 study of venetoclax + fulvestrant versus fulvestrant in patients with estrogen receptor (ER)-positive HER2-negative metastatic breast cancer (mBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-06.

Abstract PD13-06: Neoadjuvant giredestrant (GDC-9545) + palbociclib versus anastrozole + palbociclib in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer: Primary analysis of the randomized, open-label, phase II coopERA breast cancer study

Background Endocrine therapy, the therapeutic mainstay for estrogen receptor-positive breast cancer, targets estrogen receptor activity and/or estrogen synthesis. CDK4/6 inhibitors cause cell cycle arrest and significantly decrease expression of the proliferation biomarker Ki67 when used in conjunction with aromatase inhibitors such as anastrozole. Giredestrant, a highly potent, nonsteroidal, oral, selective estrogen receptor antagonist and degrader, achieves robust estrogen receptor occupancy, is well tolerated, and has encouraging antitumor activity as a monotherapy and in combination with the CDK4/6 inhibitor palbociclib in metastatic breast cancer. coopERA Breast Cancer (NCT04436744) is a phase II study investigating 2 weeks of giredestrant versus anastrozole in a window-of-opportunity phase, followed by 4 months of giredestrant plus palbociclib versus anastrozole plus palbociclib in a neoadjuvant phase in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer. We will report the results of the primary analysis. Methods Eligible patients who had measurable cT1c (≥1.5 cm)-cT4a-c estrogen receptor-positive, HER2-negative, untreated early breast cancer and baseline Ki67 score ≥5% were randomized 1:1 to 1 mg oral, daily anastrozole or 30 mg oral, daily giredestrant on Days 1-14 (window-of-opportunity phase lasting 14 days) followed by daily dosing for four 28-day cycles in combination with 125 mg oral palbociclib on Days 1-21 (neoadjuvant phase lasting 16 weeks) before surgery. Patients were stratified according to T status, Ki67 score, and progesterone receptor status. The primary efficacy endpoint was centrally assessed geometric mean relative Ki67 score change from baseline to Week 2 during the window-of-opportunity phase, which is reflective of the ability of endocrine therapies to suppress tumor-cell proliferation, and is a surrogate marker for clinical outcomes. The secondary efficacy endpoint is complete cell cycle arrest rate (CCCA), defined as Ki67 score ≤2.7%, at Week 2. Safety was also assessed. Results Results of a previous interim analysis (including 83 of the planned 202 patients) demonstrated a greater relative reduction of Ki67 at 2 weeks with giredestrant (reduction from baseline to Week 2 geometric mean = 80%; 95% CI = -85%, -72%) compared with anastrozole (reduction from baseline to Week 2 geometric mean = 67%; 95% CI = -75%, -56%; P = 0.0222). Similarly, consistent Ki67 suppression was observed in patients with baseline Ki67 ≥20% (83% reduction with giredestrant versus 71% reduction with anastrozole) or <20% (65% versus 24% reductions). At Week 2, 25% of tumors exhibited CCCA with giredestrant versus 5.1% with anastrozole (a 20% difference; 95% CI = -37%, -3%). Safety results were consistent with the known safety profile for giredestrant. Fewer patients experienced adverse events (AEs) related to giredestrant (28%) than to anastrozole (38%), and no grade ≥3 AEs or serious adverse events were assessed as related to giredestrant. We will present the results of the primary analysis, which will include data from all enrolled patients, and will report the primary and secondary efficacy endpoints (including patients with Ki67 >20%), and updated safety. Conclusions The study will proceed to the primary analysis. We expect to see encouraging results based on the favorable interim analysis data that demonstrated the superior activity of giredestrant, an oral selective estrogen receptor antagonist and degrader, compared with anastrozole.

Citation Format: Sara A Hurvitz, Vanesa Quiroga, Yeon Hee Park, Aditya Bardia, Vanesa López-Valverde, Jutta Steinseifer, Tharu M Fernando, Gonzalo Spera, Cloris Xue, Peter A Fasching. Neoadjuvant giredestrant (GDC-9545) + palbociclib versus anastrozole + palbociclib in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer: Primary analysis of the randomized, open-label, phase II coopERA breast cancer study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD13-06.

Results from VERONICA: A randomized, phase II study of second-/third-line venetoclax (VEN) + fulvestrant (F) versus F alone in estrogen receptor (ER)-positive, HER2-negative, locally advanced, or metastatic breast cancer (LA/MBC)

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Background: For patients (pts) with ER-positive, HER2-negative MBC, CDK4/6 inhibitors + endocrine therapy (ET) is standard first-line treatment, with single-agent ET considered for second-line. Nevertheless, most pts progress. A novel therapeutic target is the antiapoptotic protein BCL2, which is overexpressed in ̃85% of primary ER-positive breast cancers. VEN is a potent, selective BCL2 inhibitor that has shown promising clinical activity in pts with ER-positive and BCL2-positive MBC who have received prior ET. We report the prespecified primary and updated (for overall survival [OS]) analysis of VERONICA (NCT03584009), a phase II study of VEN + F vs F in ER-positive, HER2-negative LA/MBC. Methods: Pts were ≥18-year-old women with ER-positive, HER2-negative LA/MBC, who received ≤2 prior lines of ET and no prior chemotherapy in the LA/MBC setting and experienced disease recurrence/progression during/after CDK4/6 inhibitor therapy (received ≥8 weeks prior). Pts were randomized 1:1 to VEN (oral; 800 mg daily) + F (intramuscular; 500 mg day 1 and 15 of cycle 1; day 1 of subsequent 28-day cycles) or F, and were treated until disease progression, unacceptable toxicity, withdrawal of consent, death, or predefined study end. Pts were stratified by prior lines of therapy in the LA/MBC setting (1 vs 2) and BCL2 status (high vs low). Primary endpoint was clinical benefit rate (CBR; complete response, partial response, and stable disease ≥24 weeks). Secondary endpoints included progression-free survival (PFS) and OS; safety and exploratory subgroup analyses were also conducted. Results: At primary analysis (cutoff: Aug 5, 2020), 103 pts had been randomized (intention-to-treat [ITT] population). Median age was 58.0 and 59.5 years in the VEN + F and F arms, respectively. CBR was similar between arms (VEN + F: 11.8% [n = 6/51; 95% confidence interval (CI) 4.44–23.87]; F: 13.7% [7/51; 5.70–26.26]; risk difference: -1.96% [95% CI -16.86–12.94]). Median PFS was 2.69 months (95% CI 1.94–3.71) in the VEN + F vs 1.94 months (1.84–3.55) in the F arm (stratified hazard ratio: 0.94 [95% CI 0.61–1.45]). Results for CBR and PFS were similar in the BCL2-high and -low subgroups vs the ITT population. More grade 3–4 adverse events (AEs) were observed in the VEN + F vs F arm (n = 13/50 [26%] vs 6/51 [11.8%]). AEs observed with VEN + F were consistent with their individual safety profiles. At updated analysis (cutoff: Oct 22, 2020), OS data were not mature (35.0% event/pt ratio); median OS was 16.99 months in the VEN + F vs not reached in the F arm (stratified hazard ratio: 2.06 [1.04–4.09]). Conclusions: From the primary analysis, VERONICA did not show an improved CBR or PFS with VEN + F, vs F alone, in pts with endocrine- and CDK4/6 inhibitor-refractory LA/MBC. Biomarker analysis is ongoing. Clinical trial information: NCT03584009 .

Abstract OT-28-03: VICKI: A Phase Ib/II, randomized, placebo-controlled, study of venetoclax plus ado-trastuzumab emtansine (T-DM1) in patients (pts) with previously treated HER2-positive locally advanced (LA) or metastatic breast cancer (MBC)

Background ~15-20% of primary, invasive breast cancer (BC) overexpresses HER2 and, despite survival improvements, there remains an unmet need for further progress. The antibody-drug conjugate T-DM1 is approved for HER2-positive LA and/or MBC that has previously been treated with trastuzumab and a taxane (separately or in combination), and as adjuvant therapy for HER2-positive early BC, where there is residual invasive disease after neoadjuvant taxane and trastuzumab- or HER2-based treatment. Venetoclax (GDC-0199/ABT-199), an oral, selective small-molecule inhibitor of the antiapoptotic protein BCL-2, is approved for treatment of chronic lymphocytic leukemia, small lymphocytic lymphoma, and acute myeloid leukemia. BCL-2 may play a key role in HER2-positive BC, and venetoclax has shown promising activity in estrogen receptor-positive, BCL-2-positive MBC. We describe VICKI (Venetoclax in Combination with Kadcyla), a Phase Ib/II, randomized, double-blind, placebo-controlled, study of venetoclax plus T-DM1 in previously treated HER2-positive LA/MBC (NCT04298918).

Trial design

The study comprises a Phase Ib stage (dose escalation and expansion cohorts) and a randomized Phase II stage. Phase II will be initiated following identification of the recommended Phase II dose of venetoclax in Phase Ib (400 mg or 800 mg). Pts will be randomized 1:1 to T-DM1 (intravenous 3.6 mg/kg q3w) plus venetoclax or placebo. Randomization will be stratified per BCL-2 status (BCL-2 high vs. low), visceral disease (Yes vs. No), and HER2 immunohistochemistry (IHC) 3+ status (Yes vs. No).

Eligibility

Adult pts with HER2-positive (IHC 3+ or IHC 2+/in situ hybridization-positive), previously treated, unresectable, histologically or cytologically confirmed invasive LA/MBC are eligible. Pts will have measurable disease per RECIST v1.1 and an Eastern Cooperative Oncology Group performance status of 0 or 1. Pts in Phase II will have BCL-2 expression status by IHC (≥50% of pts BCL-2 high) and will not have received prior treatment with T-DM1, venetoclax, or anti-HER2 drug conjugates.

Aims

The Phase II co-primary efficacy endpoints will be objective response rate (ORR) and progression-free survival (PFS) per RECIST v1.1 (both investigator-assessed). Secondary and exploratory efficacy endpoints will include duration of response, overall survival, clinical benefit rate, and patient-reported outcomes. Non-efficacy endpoints will be pharmacokinetics, immunogenicity, biomarkers, and safety.

Statistical methods

In Phase II, the primary efficacy populations will include all randomized pts according to their assigned treatment arm (intention-to-treat). A point estimate and 95% CI for ORR and the difference in ORR between treatment groups will be calculated using the normal approximation to the binomial distribution. PFS will be defined as time from randomization to the first occurrence of disease progression or death from any cause. Kaplan-Meier methodology will be used to estimate median PFS. An interim analysis is planned when ~56 PFS events have occurred. Primary efficacy analysis will occur when 161 pts have had a PFS event. Cox proportional-hazards models, stratified by the stratification factors, will be used to estimate the hazard ratio with 95% CI. Safety will be analyzed per treatment received in pts who received any study treatment (safety population).

Accrual

Target accrual is ~226-284 pts at 145 sites globally (Phase Ib dose escalation: 6-24 pts; Phase Ib expansion cohorts: ~20-40 pts; Phase II: 220 pts). Accrual is ongoing.

Contact information

For more information or to refer a patient, email global-roche-genentech-trials@gene.com or call 1-888-662-6728 (USA only).

Citation Format: Geoffrey J Lindeman, Erika Hamilton, Ian Krop, Bora Lim, Shanu Modi, Cristina Saura, Rupal Desai, Bradford J Danner, Tharu M Fernando, Shengchun Kong, Fatema A Legrand, Federico Nasroulah. VICKI: A Phase Ib/II, randomized, placebo-controlled, study of venetoclax plus ado-trastuzumab emtansine (T-DM1) in patients (pts) with previously treated HER2-positive locally advanced (LA) or metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-28-03.

Functional characterization of SMARCA4 variants identified by targeted exome-sequencing of 131,668 cancer patients

Genomic studies performed in cancer patients and tumor-derived cell lines have identified a high frequency of alterations in components of the mammalian switch/sucrose non-fermentable (mSWI/SNF or BAF) chromatin remodeling complex, including its core catalytic subunit, SMARCA4. Cells exhibiting loss of SMARCA4 rely on its paralog, SMARCA2, making SMARCA2 an attractive therapeutic target. Here we report the genomic profiling of solid tumors from 131,668 cancer patients, identifying 9434 patients with one or more SMARCA4 gene alterations. Homozygous SMARCA4 mutations were highly prevalent in certain tumor types, notably non-small cell lung cancer (NSCLC), and associated with reduced survival. The large sample size revealed previously uncharacterized hotspot missense mutations within the SMARCA4 helicase domain. Functional characterization of these mutations demonstrated markedly reduced remodeling activity. Surprisingly, a few SMARCA4 missense variants partially or fully rescued paralog dependency, underscoring that careful selection criteria must be employed to identify patients with inactivating, homozygous SMARCA4 missense mutations who may benefit from SMARCA2-targeted therapy.

BCL6 Evolved to Enable Stress Tolerance in Vertebrates and Is Broadly Required by Cancer Cells to Adapt to Stress

Several lines of evidence link the canonical oncogene BCL6 to stress response. Here we demonstrate that BCL6 evolved in vertebrates as a component of the HSF1-driven stress response, which has been co-opted by the immune system to support germinal center formation and may have been decisive in the convergent evolution of humoral immunity in jawless and jawed vertebrates. We find that the highly conserved BTB corepressor binding site of BCL6 mediates stress adaptation across vertebrates. We demonstrate that pan-cancer cells hijack this stress tolerance mechanism to aberrantly express BCL6. Targeting the BCL6 BTB domain in cancer cells induces apoptosis and increases susceptibility to repeated doses of cytotoxic therapy. The chemosensitization effect upon BCL6 BTB inhibition is dependent on the derepression of TOX, implicating modulation of DNA repair as a downstream mechanism. Collectively, these data suggest a form of adaptive nononcogene addiction rooted in the natural selection of BCL6 during vertebrate evolution. SIGNIFICANCE: We demonstrate that HSF1 drives BCL6 expression to enable stress tolerance in vertebrates. We identify an HSF1-BCL6-TOX stress axis that is required by cancer cells to tolerate exposure to cytotoxic agents and points toward BCL6-targeted therapy as a way to more effectively kill a wide variety of solid tumors.This article is highlighted in the In This Issue feature, p. 565.

A dioxin response element in the multiple cloning site of the pGL3 luciferase reporter influences transcriptional activity

Luciferase reporter plasmids (pGL3 backbone, Promega) have been utilized to characterize the transcriptional effects of the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other aryl hydrocarbon receptor (AhR) ligands. Following ligand activation, the AhR and its dimerization partner AhR nuclear translocator (ARNT) regulate transcription by binding dioxin response elements (DREs) in regulatory regions of dioxin-sensitive genes. Upon sequencing of our luciferase reporters, we unexpectedly identified a DRE core motif within the multiple cloning site (mcsDRE) of the pGL3 luciferase plasmid backbone in a subset of our reporters. Therefore, the objective of this study was to determine if the mcsDRE inadvertently influences reporter activity. Utilizing deletional analysis we determined that the mcsDRE did significantly alter the transcriptional effect induced by TCDD. Since many chemicals have been shown to interact with the AhR and influence transcription through the DRE, the presence of the mcsDRE in the pGL3 luciferase plasmid may inappropriately influence promoter and enhancer analysis. As such, insertion of regulatory elements into pGL3 reporters should be designed to avoid retaining the mcsDRE core motif (GCGTG) and currently utilized pGL3 reporters should be evaluated for the presence of the mcsDRE.

2,3,7,8-tetrachlorodibenzo-p-dioxin induces transcriptional activity of the human polymorphic hs1,2 enhancer of the 3'Igh regulatory region

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an environmental toxicant known to inhibit Ab secretion and Ig expression. Inhibition of Ig expression may be partially mediated through repression of the 3'Igh regulatory region (3'IghRR). TCDD inhibits mouse 3'IghRR activation and induces aryl hydrocarbon receptor binding to dioxin response elements within the 3'IghRR enhancers hs1,2 and hs4. The human hs1,2 enhancer (hu-hs1,2) is polymorphic as the result of the presence of one to four invariant sequences (ISs), which have been correlated with several autoimmune diseases. The IS also contains a dioxin response element core motif. Therefore, the objective was to determine whether hu-hs1,2 activity is sensitive to TCDD. Using a mouse B cell line (CH12.LX), we compared the effects of TCDD on mouse hs1,2 versus hu-hs1,2 activity. TCDD inhibited mouse hs1,2 similarly to the mouse 3'IghRR. In contrast, hu-hs1,2 was activated by TCDD, and antagonist studies supported an aryl hydrocarbon receptor-dependent activation, which was replicated in a human B cell line (IM-9). Absence of Pax5 binding sites is a major difference between the human and mouse hs1,2 sequence. Insertion of the high-affinity Pax5 site in hu-hs1,2 markedly blunted reporter activity but did not alter TCDD's effect (i.e., no shift from activation to inhibition). Additionally, deletional analysis demonstrated a significant IS contribution to hu-hs1,2 basal activity, but TCDD-induced activity was not strictly IS number dependent. Taken together, our results suggest that hu-hs1,2 is a significant target of TCDD and support species differences in hs1,2 regulation. Therefore, sensitivity of hu-hs1,2 to chemical-induced modulation may influence the occurrence and/or severity of human diseases associated with hu-hs1,2.