NSABP FC-11: A phase II study of neratinib (N) plus trastuzumab (T) or N plus cetuximab (C) in patients (pts) with "quadruple wild-type" metastatic colorectal cancer (mCRC) based on HER2 status

3564

Background: Patients (pts) with KRAS wild-type (WT) mCRC treated with single agent anti-EGFR therapy (tx) have improved OS compared to BSC but only a 10-15% response rate. Prior EGFR tx may upregulate HER amplification. For pts with quadruple WT mCRC (KRAS, NRAS, BRAF, PIC3KA), data suggest that dual targeting of the MAPK pathway, specifically EGFR and HER2, may be more effective. The purpose of this study was to evaluate the activity of dual MAPK pathway inhibition based on HER2 status: amplified (amp), non-amplified (non-amp), or mutated (mt). Methods: This 2-arm phase II trial enrolled pts with quad WT mCRC with ECOG PS 0-2, adequate organ function, prior oxaliplatin- and irinotecan-based regimens, and known HER2 status. Arm 1: HER2 amp (confirmed as >2.14 copy number by Guardant 360) and prior anti-EGFR tx or HER2 mt (with qualifying mt) with or without prior anti-EGFR tx; Arm 2: HER2 non-amp or HER2 amp without prior anti-EGFR tx. Tx included T 4 mg/kg IV loading dose → 2 mg/kg/wk and N 240 mg po daily (Arm 1) or C 400 mg/m2 IV loading dose → 250 mg/m2/wk and N 240 mg po daily (Arm 2). Imaging was performed every 8 wks with response per RECIST 1.1. Primary end point (EP) of each arm was 6 mo PFS (PFS6). Secondary EPs: Response rate (ORR), clinical benefit rate (CBR), toxicity and exploratory assessments of N pharmacokinetics, genetic and molecular analyses, and evaluation of multiple drug combinations in PDX/PDXO models. We tested H0: PFS6 <0.13 v HA: PFS6 >0.47 (α=0.05; power=0.90 to reject HA). Treating 15 pts in each arm, if ≥5 pts are alive and progression free (PFS6 0.33), the arm is worth further testing. Results: From Jul 2018 - Mar 2021, 25 pts enrolled from 9 different centers. Arm 1 closed due to poor accrual (n=4). Those pts have been excluded from further analysis. Arm 2 enrolled 21 pts. with 15 evaluable for response by imaging. Early discontinuation occurred in 6 of 21 pts: 2 withdrew consent, 3 due to toxicity, and 1 physician withdrawal. Of the 15 evaluable pts, there were 6 PR, 5 of 13 HER2 non-amp, 1 of 2 HER2 amp, (duration 120-171 days; mean 140) and 5 SD (duration 59-231 days; mean 124). The ORR (CR/PR) in all pts who received at least one dose of tx is 33% (6/20). 8 of 15 evaluable pts (53%) were progression free at cycle 6. Common grade 3+ AEs (>5%) included diarrhea (24%), rash (8%), and abdominal pain/distension (8%), without any grade 5 AEs. Conclusions: The combination of C+N was reasonably well tolerated with expected toxicities of diarrhea and rash. The ORR, CBR, and PFS compare favorably to pts previously relapsed following oxaliplatin and irinotecan and treated with single-agent anti-EGFR tx. Upon entry, biopsies for PDX implantation had an engraftment success rate of ̃80%. We anticipate using these grafts to establish PDXO models for molecular analyses and further drug testing. Support: NSABP Foundation, Puma Biotechnology. Clinical trial information: NCT03457896.

NSAB C-14: CORRECT-MRD II—Second colorectal cancer clinical validation study to predict recurrence using a circulating tumor DNA assay to detect minimal residual disease

TPS3632

Background: Patients (pts) with stage II and III colon cancer (CC) have unique post-operative decisions regarding adjuvant chemotherapy (ACT). There is a subset of stage II pts with defined clinicopathologic features associated with poor prognosis who may benefit from ACT, although more discriminating and objective predictors of benefit are needed. In addition, there may be a subset of Stage III CC pts who could tolerate a de-escalation of ACT or who may require intensification of ACT to improve clinical outcome. Detectable ctDNA after resection of early-stage solid tumors has been associated with very high risk of recurrence, suggesting ctDNA is evidence of minimal residual disease (MRD). Several studies are ongoing to investigate the role of ctDNA in the optimal management of pts with CC using different assay technologies. Methods: This is a prospective, observational, multicenter study in the United States and Canada of 750 pts who have undergone complete surgical resection for stage II or III CC, have FFPE tissue available from the primary resection sufficient for a novel bespoke MRD assay, and are willing to provide serial whole blood specimens for ctDNA analysis. Subjects are asked to provide study specimens at baseline, pre-recurrence follow-up, and clinical recurrence (if applicable) study visits. ctDNA will be analyzed with an NGS-based MRD assay that identifies somatic genetic alterations from DNA derived from the pt’s tumor tissue, subtracts germline variants, and detects a subset of these tumor-specific (bespoke) ctDNA in the pt’s blood. The primary objective is to validate the association of post-definitive therapy and pre-recurrence follow-up ctDNA positivity with recurrence-free interval (RFI). Further objectives are to assess the: sensitivity and specificity of ctDNA positivity for subsequent clinical recurrence; contribution of post-surgery baseline, post-adjuvant therapy, and pre-recurrence follow-up ctDNA results on RFI; time from positive ctDNA to clinical recurrence in subjects who had a positive ctDNA result; and compare the Oncotype Colon Recurrence Score estimate of 3 yr recurrence risk with the observed 3 yr recurrence rate. The primary analysis will use a Cox proportional hazards regression applied to the RFI with ctDNA result (positive or negative) measured at post-surgical baseline (or end of ACT if ACT was used) and serially after that as a single, time-dependent covariate. Protocol: 16-002/NSABP C-14. Support: NSABP Foundation. Clinical trial information: 05210283.

NSABP FC-12: A single-arm, phase II study to evaluate treatment with gevokizumab in patients with stage II/III colon cancer who remain ctDNA+ after curative surgery and adjuvant chemotherapy

TPS3642

Background: Detection of circulating tumor DNA (ctDNA) in patients (pts) following surgery is indicative of presence of minimal/molecular residual disease (MRD) and confers a near-certain risk of disease recurrence. Therapeutic strategies to treat MRD following standard curative therapies are needed because the risk of recurrence is high and therapeutic intervention may provide clinical benefit to patients. Gevokizumab is a recombinant humanized monoclonal antibody targeting interleukin-1β (IL-1β), which is involved in all phases of the malignant process (tumorigenesis, invasion, metastasis, angiogenesis, progression, and the modulation of anti-tumor immunity). Gevokizumab has been validated in pre-clinical colon cancer (CC) models and safety established in the advanced-stage clinical setting. In this trial in progress, we aim to test the efficacy of gevokizumab in pts with early-stage CC with MRD (ctDNA-positivity) following definitive treatment. Methods: NSABP FC-12 is a single-arm, multi-centered phase II study that will include pts with stage II/III CC who test MRD+ within 6 wks following completion of curative surgery and ≥3 mos of adjuvant chemotherapy. MRD will be assessed using a personalized and tumor-informed ctDNA assay (Signatera bespoke assay). Gevokizumab will be given at a flat dose of 120 mg IV every 28 days for 13 cycles. The primary endpoint is relapse-free survival (RFS) following initiation of study therapy through one year of follow-up. Secondary endpoints are rate of ctDNA clearance at 8 wks from start of study therapy, as well as safety, toxicity, pharmacokinetics, and immunogenicity of gevokizumab. Exploratory and correlative endpoints will include outcomes associated with ctDNA clearance kinetics, tumor mutations, tumor mutational burden, circulating methylated DNA, tumor immune microenvironment profile, peripheral blood immune profile, and stool microbiome analyses. The enrollment period will be ̃12 mos. Pts will be followed for 18 mos following enrollment with ctDNA analysis at prespecified timepoints until imaging is positive for recurrence of disease or death. CT scans will be at 6-mo intervals. RFS will be determined in pts who clear ctDNA at 8 wks compared to those who do not. A single-stage design to test the null hypothesis that the 12-mo RFS is P≥0.20 versus the alternative (HA) that P≥0.35 has a sample size of 31 (alpha=0.151; power 0.811). If ≥9 of 31 pts (29%) are alive and recurrence-free at 12 mos, then gevokizumab will be considered promising for further study. Enrollment continues towards the primary endpoint. Clinical trial information: 05178576.

NSABP FC-10: A phase Ib study of pembrolizumab (pembro) in combination with pemetrexed (pem) and oxaliplatin (oxali) in patients with chemo-refractory metastatic colorectal cancer (mCRC)

3569

Background: Most pts with mCRC have microsatellite stable (MSS) disease (95%) which is unresponsive to checkpoint inhibition. Chemotherapy activity is mediated through both cytotoxicity as well as immunological effects including reduced T-regulatory cell activity, enhanced tumor antigen presentation, and induced PD-L1 tumor cell expression. Chemotherapy with checkpoint inhibitors can potentially activate T cells and alter the microenvironment to improve outcomes. Our purpose was to evaluate pembro plus pem in a safety run-in (cohort 1) and the same with dose-escalated oxali (cohort 2). Methods: Eligible pts with MSS mCRC had ECOG PS of 0-1, measurable metastatic disease, adequate organ function, and prior treatment with fluoropyrimidine-, oxali-, and irinotecan-based therapies (plus an anti-EGFR agent, if apropos). Cohort 1 treatment was pem 500 mg/m2 IV plus pembro 200 mg IV every 3 wks. Cohort 2 treatment was the same, plus oxali at an escalating dose of 85-120 mg/m2 utilizing a 3+3 design with expansion of 6 additional pts at the RP2D. Imaging was performed every 3 cycles; response was determined by RECIST 1.1. Primary endpoint (EP) of each cohort: safety and best ORR with cohort 2 also to establish the RP2D. Secondary EPs: Clinical benefit rate (CBR), PFS, OS at 1 year, and exploratory assessments of circulating immunologic profiles and molecular predictors of response. Descriptive statistics were planned as a signal-seeking study. Results: From Jul 2019-Apr 2021, 34 pts enrolled from 4 different centers. In cohort 1 (n=15), one pt was taken off study due to LFT elevation and orchitis attributed to pembro with reduced lymphadenopathy upon withdrawal. There was 1 PR (duration 686 days) and 4 SDs (61, 66, 124, 128 days) among 11 evaluable for response. There were no unexpected nor grade 5 toxicities. In cohort 2 (n=19), 2 pts achieved a PR (127 and 185 days), with SDs in 5 (59, 63, 69, 115, 437), among 13 evaluable for response. At oxali dose of 85 mg/m2, 1/6 pts had DLT (grade 4 neutropenia ≥7 days); another 1/6 pts had DLT at 120 mg/m2 (grade 3 AST/ALT). The RP2D was 120 mg/m2. Common grade 3/4 AEs included: neutropenia (24%), anemia (9%), fatigue (9%), abdominal pain (6%), nausea (6%), and ALT/AST (6%). There was no febrile neutropenia nor any grade 5 events. Combined cohort rates of PR/CBR were 3/24 (12.5%) and 12/24 (50%), respectively. Conclusions: In this study of heavily pretreated pts with MSS mCRC, combining pembro plus pem or pem+oxali was well tolerated. Overall CBR was 50%, with objective responses (PRs) in 3/24 (12.5%) evaluable pts. This compares favorably with KEYNOTE 016, in which pembro in MSS mCRC pts had 0/18 objective responses and CBR=11% (2/18). Further studies testing these agents in earlier lines of treatment with robust correlative analyses is supported. Support: NSABP Foundation; Merck; Lilly. Clinical trial information: NCT03626922.

Results of a phase II randomized trial of cisplatin +/- veliparib in metastatic triple-negative breast cancer (TNBC) and/or germline BRCA-associated breast cancer (SWOG S1416)

1001

Background: PARP inhibitors(i) are effective in BRCA-mutation -associated metastatic breast cancer(MBC). However, there are no studies evaluating PARPi + platin chemotherapy in BRCA wild-type(wt) TNBC. Approximately 1/2 of BRCAwt TNBC demonstrate homologous recombination deficiency (HRD) resulting in a BRCA-like phenotype which might render them sensitive to PARPi. S1416 compared the efficacy of cisplatin plus PARPi veliparib (Vel) or placebo (P) in 3 groups of MBC: gBRCA+; BRCA-like; and non-BRCA-like. Methods: Patients (pts) with metastatic TNBC or g BRCA1/2-associated MBC, who had received < 1 line of prior therapy were treated with cisplatin (75mg/m2) plus Vel or P (300 mg po BID days 1-14), every 3 weeks. All pts underwent central gBRCA testing. A priori established multipronged biomarker panel was used to classify BRCAwt pts into BRCA-like and non-BRCA-like groups, and included myChoice HRD score, somatic BRCA1/2 mutations, BRCA1 methylation and non- BRCA1/2 HR germline mutations. Primary end-point was progression-free survival (PFS) in the three pre-defined groups; secondary end-points included objective response rate (ORR), overall survival (OS), toxicity. Results: 323/335 randomized pts were eligible for efficacy evaluation; 31% had received 1 prior chemotherapy for MBC. 248 pts were classified into the three groups: (1) 37 gBRCA+ (2) 101 BRCA-like; (3) 110 non- BRCA-like. Remaining 75 could not be classified due to missing biomarker information. In the gBRCA+ group (which reached 62% of its projected accrual), numerically better PFS was noted with Vel compared to P (HR=0.64; p=0.26) though this difference was not statistically significant. In BRCA-like group improved PFS was noted with Vel vs P (median PFS 5.7 vs 4.3 months HR=0.58; p=0.023, 1 years PFS 20% vs 7%). Numerically better OS (median OS 13.7 vs 12.1 months, HR=0.66; p=0.14) and ORR (45% vs 35%, p=0.38) were noted with Vel vs P in BRCA-like group. Non-BRCA-like group did not show benefit of veliparib for PFS (HR=0.85; p=0.43) neither did the unclassified group (HR=0.97). Grade 3/4 neutropenia (46% vs 19%) and anemia (23% vs 7%) occurred at higher frequency in Vel arm compared to P. Conclusions: Addition of Vel to cisplatin significantly improved PFS and showed a trend towards improved OS for BRCA-like advanced TNBC. Integral biomarkers used in this study identified a subgroup of BRCAwt TNBC who benefited from addition of PARPi to cisplatin; platinum plus PARPi combination should be explored further in BRCA-like TNBC. Clinical trial information: NCT02595905 .

Biomarker analysis of PALLET: A neoadjuvant trial of letrozole (L) ± palbociclib (P)

570

Background: PALLET randomized 307 postmenopausal women with ER+ primary breast cancer to one of 4 treatment groups (3:2:2:2 ratio): A: L for 14wks; B: L for 2wks then L+P to 14wks; C: P for 2wks then L+P to 14wks; D: L+P for 14wks. This allowed a randomized 1:2 comparison of L (Group A) vs L+P (Groups B+C+D) at 14wks. P was given 125mg/d PO (21 days on, 7 days off). Adding P to L markedly enhanced Ki67 suppression and Complete Cell Cycle Arrest (CCCA, Ki67 < 2.7%) by 14wks but did not substantially increase clinical response. We now report exploratory analysis of the association of baseline expression of 6 pre-specified biomarkers involved in estrogen and CDK4/6 signaling with CCCA at 14wks and changes in their expression during therapy. Methods: Estrogen receptor (ER), progesterone receptor (PgR), RB and CCNE1 were measured by IHC and CCND1 by IHC and FISH (CCND1/CEP11 ratio≥2.0 amplified). Baseline biomarker values were available with 14wk Ki67 values in up to 64 patients for L alone and up to 124 patients for L+P. Of these 59% and 90%, respectively, achieved CCCA. Results: With L alone CCCA was significantly less frequent (indicating relative resistance) with low baseline PgR (odds ratio [OR] 0.22, 95%CI 0.05-0.96, p = 0.04) or high CCNE1 levels (OR 10.39, 95%CI 1.19-90.48, p = 0.03). With L+P CCCA was also significantly less frequent with high CCNE1 (OR 50.34 95%CI 5.12-495.34, p = 0.001) or with low baseline ER (OR 0.21 95%CI 0.08-0.60, p = 0.004). CCCA was not significantly different with either treatment according to CCND1 amplification status or expression overall. However, CCCA showed a tendency to being less frequent in non-amplified cases with low baseline cyclin-D1 expression when treated with L+P (p = 0.10). There were no significant changes in ER levels or CCND1 amplification over 14wks. By 14 wks PgR, RB, CCND1 and CCNE1 levels were significantly suppressed by L or L+P (geomeans PgR: -96.4% vs -94.9%; CCND1: -79.9% vs -70.7%; CCNE1: -68.2% vs -74.7%; RB: -23.5% vs 26.1%, respectively) and there was no significant difference between the treatments. Conclusions: These data support low ER, possibly indicating limited luminal status, and high CCNE1 as markers of poor Ki67 response to L+P in primary disease and are consistent with findings in studies in advanced disease. Clinical trial information: NCT02296801.

Number of tumor-infiltrating lymphocytes in breast cancer brain metastases compared to matched breast primaries

2049

Background: Breast cancer brain metastasis (BCBM) is frequent in advanced disease, has limited therapies, and is associated with poor prognosis. Increased stromal tumor infiltrating lymphocytes (sTILs) are prognostic in triple-negative breast cancer (TNBC) and predictive of therapeutic response in early breast cancer (BC). However, little is known about sTILs in the metastatic setting. We compared %sTILs between the largest known cohort of matched primary tumors and BCBM and correlated the results with clinical endpoints. Methods: We retrospectively investigated 37 matched primary tumors and BCBM tissue from three institutions. In addition, we identified 29 primary tumors from patients later diagnosed with BCBM. H&E-stained sections were manually measured for %sTILs using standard criteria. Wilcoxon signed rank tests assessed for changes in %sTILs between primary and metastatic lesions. A Cox proportional hazards model was used to determine if %sTILs in the breast tissue predicts time from primary tumor biopsy to diagnosis of brain metastasis (TTDBM) while adjusting for clinicopathologic features. Results: Average age at time of BCBM diagnosis was 53.6 (SD 12.3). 52% (34/66) of primary tumors were hormone receptor (HR) positive. Of 60 patients with known HER2 status, 28% (17) were HER2 positive and 40% (24) TNBC. Median %sTILS was significantly different between all primary tumors (15, IQR 5-20) and brain metastases (10, IQR 5-10), p = 0.001. The TNBC subtype (n = 11) showed the largest decrease in %sTILs between primary tumors (20, IQR 10-20) and brain metastases (5, IQR 5-10), p = 0.022. Comparing primary tumors and brain metastases, there was a 5% decrease in %sTILs in HR-/HER2+ (n = 5, p = 0.13) and HR+/HER2- (n = 7, p = 0.13), and a 5% increase in %sTILs in the HR+/Her2+ subtype (n = 9, p = 0.69). Percent sTILs in the primary tumors was not a significant predictor of TTDBM, when adjusting for race, age, HR status, and HER2 status, p = 0.87. Conclusions: BCBM have a significantly decreased %sTILs compared to their primary tumors, most prominent in TNBC. These results suggest altered tumor immunogenicity in the metastatic setting which has broad implications for the development of immunotherapy.

Incidence of febrile neutropenia with use of docetaxel plus cyclophosphamide (TC) for breast cancer

e12073

Background: Incidence of febrile neutropenia (FN) is reported as 5% in breast cancer patients receiving TC (Jones et al., JCO 2006), which would not justify the usage of prophylactic granulocyte colony stimulating factors (G-CSF). We previously showed that the incidence of FN may be as high as 23% in a small study. (N = 130, Soni et al., ASCO 2011). In the current study, we determined the incidence of FN in a larger cohort (N = 415), and evaluated the usage of G-CSF and its relation to FN, age, stage, and hormonal status. Methods: We retrospectively reviewed the electronic medical records from patients diagnosed with breast cancer who received at least one standard dose cycle of adjuvant TC between 2010-2016 at a university-based breast oncology practice. Chi-square or Fisher’s exact tests were used to assess differences between groups. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using multiple logistic regression models. Results: We identified in total 415 patients who received adjuvant TC. Median age at diagnosis was 58 (range: 25-86), the majority had stage I or II (N = 382; 92.1%) disease, and 315 (75.9%) were ER+, 277 (66.8%) PR+, 42 (10.1%) HER2+, 22 (5.3%) triple-positive, and 81 (19.5%) triple-negative. Prophylactic G-CSF was utilized in 247 patients (59.5%), and unknown for 43 (10.4%). Overall 39 (9.4%) patients experienced febrile neutropenia. Incidence of FN among those receiving G-CSF was 4.5% versus 17.6% among those who did not (p < 0.001). Use of G-CSF significantly lowered risk of FN, OR (95%CI): 0.20 (0.10-0.43) adjusted for age at diagnosis and stage. Use of G-CSF on incidence of FN did not differ significantly by age, stage, or hormonal status. Conclusions: Our data confirms a high rate of FN in patients receiving TC without G-CSF prophylaxis. Our institutional high rate of G-CSF use ( > 50%) reduced the incidence of FN to 4.5% and the observed significant difference in FN incidence between the non G-CSF group and G-CSF group suggests that prophylaxis may be considered when administering TC. Age, stage, and hormonal status do not seem to affect the usage of G-CSF or incidence of FN in our population.

cfDNA mutation frequency in early stage breast cancer

e23047

Background: Though 93% of patient present with early stage breast cancer (EBC), metastatic recurrence is expected in 7-13%. To prevent estrogen receptor (ER) positive disease recurrence, endocrine therapy (ET) is given after local disease. ET guidelines recently extended therapy —specifically tamoxifen—from 5 years to 10 based on ATLAS and aTTom. This pilot study used blood samples from women 6 months post-ET to determine cell free DNA (cfDNA) mutation prevalence in disease-free patients Methods: Patients with EBC and continued follow-up after ET were recruited from the Magee Women’s Breast Cancer Clinic. Inclusion criteria were EBC, ER+, and completion of ET > 6 months prior to visit; the exclusion criterion was active disease. Patients gave 2 blood samples, placed in Streck and EDTA tubes and processed at 2 laboratory sites for cfDNA. Blood from patients with metastatic breast cancer (MBC) served as controls for mutation detection. cfDNA was amplified for ESR1 and PIK3CA genes. Targeted amplifications underwent digital droplet PCR to identify mutations: 4 for ESR1 (D538G, Y537C/N/S), 2 for PIK3CA (E545K, H1047R) Results: Ten EBC patients > 6 months post-ET (post-EBC; 2/5/3 of stage I/II/III) and 10 MBC patients gave samples. cfDNA yield between plasma isolated from EDTA and Streck tubes (including mutation allele frequencies) was not significantly different (p > 0.05); cfDNA yield from patients with MBC was > 2X higher than post-EBC (p < 0.001). MBC cfDNA had 2 monoclonal and 1 polyclonal (2 different) mutations in ESR1, while post-EBC cfDNA had none Conclusions: This pilot study shows cfDNA can be consistently isolated from Streck or EDTA-processed blood from patients with MBC and post-EBC; however, cfDNA levels are significantly higher in MBC. There were no mutations (ESR1 or PIK3CA) in post-EBC samples, though ESR1 mutations were found in MBC. Further studies are needed to determine if mutations in cfDNA can be found in patients without evidence of disease

Phase III randomized, placebo-controlled trial of carboplatin (C) and paclitaxel (P) with/without veliparib (ABT-888) in HER2- BRCA-associated locally advanced or metastatic breast cancer (BC)

155

Background: BRCA-mutated tumors are more susceptible to platinum therapy and PARP inhibitors due to underlying defects in homologous recombination repair of DNA damage. In preclinical models the potent oral PARP1/2 inhibitor veliparib was shown to enhance sensitivity to C and to have single-agent activity in BRCA+ cell lines. Phase 1 trials suggest promising antitumor activity and acceptable toxicity of veliparib plus C/P in triple-negative BC (Puhalla et al. Cancer Res 2012;72:PD09-06) and single-agent activity of veliparib in BRCA+ BC (Somlo et al. J Clin Oncol 2014;32:abstr. 1021). This phase III trial assesses efficacy and toxicity of veliparib plus C/P vs C/P alone in patients with HER2− BRCA-associated locally advanced or metastatic BC (NCT02163694). Methods: Phase III randomized, double-blind, placebo-controlled, multicenter trial. Eligible patients (female or male; ≥ 18 years) have HER2−metastatic/locally advanced unresectable BC with (suspected) deleterious BRCA1/2 germline mutations and received 2 or fewer prior lines of DNA-damaging chemotherapy for metastatic BC. In addition, patients must have received ≤ 1 prior line of platinum therapy (any setting) without progression within 12 months of completing treatment. Patients are randomized 2:1 to C/P with veliparib or C/P with placebo, stratified by estrogen and/or progesterone receptor expression, prior platinum therapy, and central nervous system metastases. Veliparib (120 mg p.o. BID) or placebo will be given on Days −2 to 5, C (AUC 6 mg/mL/min i.v.) on Day 1, and P (80 mg/m2i.v.) on Days 1, 8, and 15 (21-day cycles). Treatment continues until unacceptable toxicity or progressive disease (PD). Patients in the placebo arm who discontinue due to PD are eligible for crossover to veliparib monotherapy. The primary objective is to assess if the addition of veliparib to C/P increases progression-free survival; additional objectives include evaluation of overall survival, clinical benefit rate, objective response rate, quality of life, and safety. Enrollment began in July 2014 with a planned sample size of 270 patients. Clinical trial information: NCT02163694.

Clinical effects of prior trastuzumab on combination eribulin mesylate plus trastuzumab as first-line treatment for HER2+ locally recurrent or metastatic breast cancer (MBC): Results from a phase 2, single-arm, multicenter study

139

Background: Eribulin mesylate, a novel nontaxane microtubule dynamics inhibitor in the halichondrin class of antineoplastic drugs, is indicated for women with MBC who previously received ≥ 2 chemotherapy regimens in the metastatic setting. Primary data from a phase 2 trial on first-line combination eribulin + trastuzumab (TRAS) in HER2+ patients (pts) showed a 71% objective response rate (ORR) and tolerability consistent with the known profile of these agents. Here we present prespecified endpoint data for this study by prior TRAS use. Methods: Pts with HER2+ MBC who had not received prior chemotherapy for MBC received eribulin mesylate 1.4 mg/m2 IV on days 1 and 8 of each 21-day cycle and initial TRAS (8 mg/kg IV/day 1), followed by 6 mg/kg/day 1 of each subsequent cycle. Response, progression-free survival (PFS), and tolerability were assessed in patients who had and had not received prior TRAS treatment. Results: The 52 pts (median age, 59.5 years) received combination eribulin + TRAS, for a median treatment duration of ~30 weeks; 40% (n=21) were previously treated with TRAS in the neo-adjuvant/adjuvant setting. There was median of 23 months since completion of adjuvant treatment prior to retreatment with eribulin + TRAS for first-line MBC.Efficacy, assessed by ORR, clinical benefit rate (CBR), PFS, and duration of response (DOR), was largely consistent in pts who received prior TRAS relative to pts who had not received prior TRAS (see table). Overall, grade (G) 3-5 adverse events (AEs), treatment-related AEs (TRAEs), and discontinuations (d/c) were similar between groups (Table). Conclusions: In this phase 2 single-arm trial in pts with HER2+ MBC, eribulin + TRAS demonstrated activity and was well tolerated as first-line treatment, irrespective of prior (neo) adjuvant TRAS treatment. Clinical trial information: NCT01269346. [Table: see text]

Clinical effects of prior anthracycline or taxane use on eribulin as first-line treatment for HER+/- locally recurrent or metastatic breast cancer (BC): Results from 2 phase 2, multicenter, single-arm studies

140

Background: Eribulin mesylate, a nontaxane microtubule dynamics inhibitor, has demonstrated an overall survival benefit relative to other commonly used agents in patients (pts) with at least 2 prior MBC cytotoxic therapies. Primary data presented from 2 phase 2 trials, Study 206 (eribulin in HER2- BC pts) and Study 208 (combination eribulin + trastuzumab [TRAS] in HER2+ BC pts), showed clinical activity and acceptable tolerability profiles as first-line cytotoxic therapy (tx). Here we present prespecified efficacy data for both trials based on prior anthracycline (A) and taxane (T) use. Methods: In both studies, pts received eribulin mesylate 1.4 mg/m2 IV on days 1 and 8 of each 21-day cycle. Pts in Study 208 (HER2+) also received initial TRAS (8 mg/kg IV/Day 1), followed by 6 mg/kg/day 1 of each subsequent cycle. Objective response rate (ORR), progression-free survival (PFS), and tolerability were assessed. Results: In Study 206 (N=56), 48% and 46% received prior A and T, and in Study 208 (N=52), 21% and 44% received prior A and T, respectively. ORR, the primary endpoint, was similar in pts, regardless of prior A or T, except in pts w/o prior T in Study 208 whose ORR trended higher (table). Clinical benefit rate (CBR), PFS, and duration of response (DOR) were either similar or trended higher in pts w/o prior A or T. PFS was higher in HER2+ BC patients receiving eribulin + TRAS who had not received prior A or T compared with those who had. Grade (G) 3-5 adverse event rates were similar or lower in pts who had not received prior A or T. Conclusions: As first-line therapy, eribulin in HER2- BC pts and eribulin + TRAS in HER2+ BC pts were effective and well tolerated, regardless of prior A or T tx. However, in HER2+ BC pts receiving eribulin + TRAS, the lack of prior A or T tx may be a lead to longer median PFS. Clinical trial information: NCT01268150/NCT01269346. [Table: see text]

A phase I study of chronically dosed, single-agent veliparib (ABT-888) in patients (pts) with either BRCA 1/2-mutated cancer (BRCA+), platinum-refractory ovarian cancer, or basal-like breast cancer (BRCA-wt)

3054

Background: Veliparib (ABT-888) is an oral, potent inhibitor of PARP 1/2. Preclinically, PARP inhibitors have activity in tumors with defective homologous recombination (HR), particularly those that are BRCA+. Reduced levels of BRCA expression have been observed in ovarian cancer and basal-like breast cancer, which share genotypic and phenotypic similarities with BRCA+ cancers. We postulated that these tumors types may be similarly sensitive to single-agent PARP inhibition. This study sought to establish the maximum tolerated dose (MTD), dose limiting toxicities (DLT), pharmacokinetic and pharmocodynamic properties, and preliminary efficacy of chronically-dosed veliparib. Methods: A 3+3 dose escalation phase I trial was performed. Nine dose levels (DL) were planned, and dose escalation started at 50 mg BID to a maximum of 500 mg BID. Veliparib was administered orally continuously on a 28 day cycle. Results: 63 pts have been enrolled to date. Thirty-eight were BRCA+ (20 ovary, 12 breast, 2 pancreas, and one each - prostate, peritoneal, fallopian tube, endometrial); 25 BRCA-wt. (21 breast, 4 ovarian). DLTs occurred at the following dose levels: BRCA+: gr. 2 thrombocytopenia at 50 mg BID; BRCA+: gr.3 Nausea/vomiting at 400 mg BID; BRCA-wt: gr 2 seizure at 400 mg BID. The MTD has not been determined and 500 mg BID is presently enrolling. Notable toxicities have included low-grade fatigue and nausea. PK was linear and non-saturable with t ½ of 5 h. The number of cycles administered ranged from 1- 15, median 2. In BRCA+ pts, there were 2 partial responses (breast, ovarian) and 10 pts had evidence of prolonged SD ≥ 4 months. In BRCA-wt pts, there was 1 PR (breast) and 7 pts with SD≥ 4 months. Correlative studies, including assessment of PAR inhibition and BRCA methylation status, are ongoing. Conclusions: Veliparib is tolerable on a continuous oral dosing schedule with evidence of anti-tumor activity seen in BRCA+ and BRCA-wt tumors. A mandatory biopsy expansion cohort is planned at the recommended phase II dose, which will allow further insights regarding efficacy and mechanisms of resistance to PARP inhibition.

ABT-888 (veliparib) in combination with weekly carboplatin and paclitaxel in advanced solid tumors

TPS1138

Background: The combination of paclitaxel and carboplatin is widely used for the treatment of patients with advanced solid tumors of diverse histologies. In breast cancer patients, a weekly regimen of paclitaxel has shown greater efficacy with comparable safety, when compared to every-three-weeks dosing (ECOG 1199). ABT-888 (veliparib) is an oral inhibitor of poly-ADP-ribose polymerase (PARP). Inhibition of PARP has been shown in preclinical studies to potentiate the effect of cytotoxic agents which induce DNA damage, such as platinum agents. The preclinical synergy of carboplatin with veliparib and the efficacy of the combination of paclitaxel with carboplatin supports exploration of this triplet regimen. Methods: This 3+3 phase I trial will seek to determine the maximum tolerated dose (MTD) of the combination of carboplatin (AUC 2), paclitaxel (80 mg/m2), and veliparib in patients with advanced solid tumors. Veliparib will be escalated beginning at 50 mg PO BID to a maximum of 200mg PO BID. Treatment will be given on a weekly basis over a 21-day cycle. There will be an expansion cohort of 6-12 patients with triple negative breast cancer at the maximum tolerated dose. This group of patients will undergo mandatory pre- and post-cycle 1 tumor biopsies. Secondary aims of the study include safety and toxicity of the combination, its pharmacokinetic and pharmacodynamic effects, documentation of any anti-tumor response, and assessment of the characteristics of the tumor specimens obtained in the expansion cohort that may contribute to efficacy. The latter will include whole genome microarray analysis to evaluate expression of genes involved in DNA repair pathways. Currently, the recommended phase II dose has not been determined and enrollment is ongoing on the last planned dose level (veliparib 200 mg BID).