Risk assessment model potency to detect patients most likely to benefit from thromboprophylaxis: An application of the TARGET-TP score

12116

Background: Interventional trials applying risk models for targeted-thromboprophylaxis (TP) for ambulatory cancer patients have previously excluded low risk patients, preventing quantification of residual risk and unmet need. We compare potency and pragmatic application of risk models, to guide routine clinical utilisation. Methods: TARGET-TP, a three arm phase 3 randomized trial of TP, classified ambulatory lung and gastrointestinal cancer patients into high or low thromboembolism (TE) risk groups using an algorithm derived from fibrinogen and d-dimer levels. High risk patients (randomized arms) received enoxaparin or no TP. Low risk patients were enrolled as an observation arm. Risk model potency was assessed by comparing cumulative TE incidence at 180 days between the two arms not receiving enoxaparin. In this analysis, we also compared other risk models using published risk thresholds (Khorana Score (KS), PROTECHT, CONKO, CATS/MICA) using associations of predicted TE risk with observed TE events (cause specific Cox proportional hazards regression), sensitivity and specificity. Results: Among 328 patients, 200 (61%) were classified high TE risk using the TARGET-TP algorithm. Without TP, TE incidence was 23% among high risk and 8% low risk patients – compared to 8% in high risk enoxaparin treated patients. There was notable cohort migration, with individual patients reclassified between high- and low-risk across other risk. Up to 75% of TARGET-TP high risk patients were classified low risk by other models, and would not be considered for TP, potentially exposing substantive residual TE risk (75% low risk by CATS/MICA, 61% KS, 60% CONKO, 32% PROTECHT). Up to 57% of low risk patients were high risk by other models, potentially exposing unnecessarily to TP (57% high risk by PROTECHT, 27% KS, 26% CONKO, 5% CATS/MICA). Among 228 patients in TARGET-TP trial non-intervention arms: TE incidence and comparative risk (hazard ratio, HR) for high versus low TE risk were: TARGET-TP (23% high vs. 8% low, HR 3.33 [95%CI 1.58-6.99]), KS (17% vs. 13%, HR 1. 50 [95%CI 0.74-3.02]), PROTECHT (16% vs. 12%, HR 1.50 [95%CI 0.69-3.05]), CONKO (18% vs. 13%, HR 1.54 [95%CI 0.76-3.09]), CATS/MICA (26% vs. 12%, HR 2.72 [95%CI 1.26-5.86]). Sensitivity and specificity respectively: TARGET-TP 70%/61%, KS 39%/68%, PROTECHT 70%/37%, CONKO 39%/69%, CATS/MICA 27%/87%. Conclusions: Application of TE risk models demonstrated some ineffectual and if utilised to define TP eligibility, 4/5 would exclude patient cohorts with TE rates exceeding 10%. TARGET-TP was the only model to achieve both high sensitivity and specificity. This simple pragmatic model considers only d-dimer and fibrinogen, can be applied without complex calculations or nomograms, in real-time for any patient. Clinical trial information: ACTRN12618000811202.

Targeting HER2-positive metastatic breast cancer with ARX788, a novel anti-HER2 antibody-drug conjugate in patients whose disease is resistant or refractory to T-DM1, and/or T-DXd, and/or tucatinib-containing regimens

TPS1112

Background: The overexpression and/or amplification of human epidermal growth factor receptor 2 (HER2) occurs in approximately 20% of breast cancers (BC) and is a major driver of tumor development and progression. This HER2 subtype confers aggressive tumor behavior and the HER2 receptor remains a valuable target for antibodies, bi-specifics, and antibody drug conjugates (ADC). With advances in targeted therapy, patients with HER2-positive breast cancer (HER2+ BC) may experience an improved prognosis, including survival. Novel HER2-targeted therapies are being investigated to overcome drug resistance and to help mitigate adverse events (e.g., cardiotoxicity). ARX788 is a next-generation ADC using a technology platform whereby a HER2 specific monoclonal antibody is conjugated with Amberstatin269 (AS269), a potent cytotoxic tubulin inhibitor. Site-specificity, high homogeneity, and stable covalent conjugation of ARX788 leads to its slow release and prolonged peak of serum pAF-AS269, which may contribute to the lower systemic toxicity and increased targeted delivery of payload to tumor cells at a lower effective dose compared to other HER2 ADCs. Clinical activity has been seen in Phase I HER2 breast and pan-tumor studies. Methods: Trial Design: ACE-Breast-03 (NCT04829604) is a global, phase 2 study designed to assess anticancer activity and safety of ARX788 in patients with metastatic HER2 positive breast cancer. Patients whose disease is resistant or refractory to T-DM1, and/or T-DXd, and/or tucatinib-containing regimens are eligible. Patients must have adequate organ function. Any brain metastases must be radiographically stable without steroid dependence. Efficacy will be assessed using Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 by imaging every 6 weeks on study. Endpoints include objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), best overall response (BOR), duration of response (DOR), and time to response (TTR). The safety and tolerability profile will be evaluated. Blood samples will be collected at specified time points to determine serum concentrations of ARX788, total antibody, and metabolite pAF-AS269. Potential predictive and/or prognostic biomarkers at baseline and on-treatment will be analyzed for exploratory purposes. Descriptive statistics will be used to evaluate anticancer activity, safety, and tolerability. The study is currently recruiting patients. Please contact breast03trialinquiry@ambrx.com for additional information. Clinical trial information: NCT04829604.

A randomized, open-label, phase 3 study of low-dose selinexor and lenalidomide (Len) versus len maintenance post autologous stem cell transplant (ASCT) for newly diagnosed multiple myeloma (NDMM): ALLG MM23, Sealand

TPS8055

Background: Len maintenance post ASCT is standard of care for patients (pts) with NDMM. Deep responses (CR or better) post ASCT correlates with better progression free survival (PFS). In a meta-analysis of len maintenance post ASCT (McCarthy PL et al. J Clin Oncol. 2017), only 10.7% of pts achieve CR post ASCT, and 72% of pts who discontinued len maintenance did so because of progressive disease (PD). Selinexor is a selective inhibitor of nuclear export that blocks exportin 1, thus retaining tumour suppressor proteins within the nucleus while blocking proto-oncoprotein translation. It is approved in combination with bortezomib and dexamethasone (dex) for pts with MM who have had at least 1 prior line of treatment, or with dex for pts with penta-refractory MM by the FDA. The oral bioavailability and weekly schedule of selinexor makes it suitable in combination with len for maintenance therapy. Given the encouraging activity (ORR 92%) and tolerability of selinexor, len and dex from the phase 1b/2 STOMP study, we hypothesise that combination low-dose selinexor and len (XR) will be well tolerated and effective, increasing CR and MRD negativity rate post ASCT, thus prolonging PFS compared to len. Methods: ALLG MM23 SeaLAND, is an ongoing randomised, multi-centre, phase 3 trial. Eligible pts ( > 17 years of age) have measurable disease, have undergone 3-6 cycles (C) of induction containing a proteasome inhibitor (PI) and/or immunomodulatory drug and recovered post melphalan-conditioned ASCT with adequate haematopoiesis, renal and liver function, and with ECOG performance status. Registration occurs prior to ASCT with screening between 75 to 115 days post ASCT. The study includes a lead-in safety phase of 20 patients with XR: Len 10mg daily days 1 to 21 and Selinexor 40mg weekly in a 28-day cycle. If well tolerated, Selinexor escalates to 60mg po weekly from C2 and Len to 15mg po daily from C4. Two safety reviews will occur after the 10th and 20th patients completes C2, respectively. Upon meeting safety criteria, a sample size of 290 pts will be randomised 1:1 to XR or lenalidomide (R). Therapy will continue until PD. The primary endpoint is PFS at 3 years post randomisation. Secondary endpoints include ORR and MRD-negativity rate (International Myeloma Working Group Response Criteria), PFS on next treatment line (PFS2), OS, safety and tolerability, quality of life, and cost effectiveness. Main analysis occurs after 232 patients complete 3-years of follow-up. Exploratory objective is to correlate immunological and molecular profiles to treatment response and resistance. ALLG MM23 SeaLAND is a multisite bi-national investigator-initiated trial lead by Australia and New Zealand’s national cooperative group, the Australasian Leukaemia & Lymphoma Group. Clinical trial registration: ACTRN12620000291987p. Clinical trial information: 12620000291987.

Safety and unique pharmacokinetic profile of ARX788, a site-specific ADC, in heavily pretreated patients with HER2-overexpresing solid tumors: Results from two phase 1 clinical trials

1038

Background: ARX788 is a site-specific, homogeneous, and highly stable ADC. The payload AS269 is conjugated to the synthetic amino acids para-acetylphenylalanine (pAF) in a humanized anti-HER2 mAb. ARX788 demonstrated promising activity in HER2-positive, HER2-low, and T-DM1 resistant tumors in preclinical studies. Here we present the phase 1 clinical data evaluating the safety, antitumor activity, and PK of ARX788 in advanced solid tumors. Methods: The standard 3+3 design (0.33 - 1.5 mg/kg; Q3W or Q4W) is used to determine the MTD and/or RP2D in two phase 1 studies in HER2-positive solid tumors in U.S. and Australia (ACE-Pan tumor-01) and in HER2-positive breast cancers in China (ACE-Breast-01). The efficacy endpoints include ORR and DCR. Intensive PK sampling in first 3 cycles is performed to characterize serum PK profiles of ARX788, total Ab, and pAF-AS269. Results: 69 and 34 heavily pretreated patients received ARX788 monotherapy in the ACE-Breast-01 (median 6 prior lines of therapy) and ACE-Pan tumor-01 trial (including breast, gastric/GEJ, NSCLC, ovarian, urothelial, biliary track, endometrial, and salivary gland cancer) respectively. Dose escalation for both studies have been completed with no DLT reported. MTD has not been reached. ARX788 was generally well tolerated with most AEs being grade 1 or 2. The most common grade >3 AEs include ocular AEs (5.7 %) and pneumonitis (4.3%) in the ACE-Breast-01 trial; pneumonitis (2.9%) and fatigue (2.9%) in the ACE-Pan tumor-01 trial. Low systemic toxicities in terms of the incidence rate and grade (as shown in table). No treatment-related death. In the 1.5 mg/kg cohort, ORR was 74% (14/19) and 67% (2/3) for ACE-Breast-01 and ACE-Pan tumor-01, respectively. DCR was 100%. Median DOR or median PFS has not been reached. PK profiles for total antibody and ARX788 were generally comparable across all dose levels. Mean T1/2 for ARX788 and total antibody had approximately 100 hours at the dose of 1.5 mg/kg. Serum pAF-AS269 concentrations peaked with a median time of 168 h. Serum exposure of pAF-AS269 was low with the Cmax and AUC at cycle 1 being approximately 0.1% and 0.18% of those for ARX788 on a molar basis, respectively. Conclusions: High stability of ARX788 and low serum exposure of pAF-AS269 may underlie the low systemic toxicity, which differentiates it from other ADCs. Clinical trial information: NCT032550070 .[Table: see text]

Extended survival in 80 patients with operable, locoregionally recurrent breast cancer treated with chemotherapy

Locoregional recurrence is a harbinger of disseminated disease, and historically the estimated 5-year survival when treated with local therapy only varies between 21% and 37%. The role of systemic treatment after local treatment is unclear at present. The authors investigated the results of systemic chemotherapy for these patients after complete local surgical resection. Data on 80 patients were evaluable for toxicity, time to treatment failure (TTF), and survival. Sixty-four patients received doxorubicin-based treatments, four received methotrexate-based combinations, and 12 received tamoxifen only. Among the 68 patients treated with cytostatics, there were two possible treatment-related deaths. Two patients developed grade 3 neutropenia, four developed grade 3 vomiting, and 42 had grade 2 toxicity. The 2- and 5-year disease free survival at a mean follow-up period of 5.5 years were 56% and 38%, respectively. The projected median TTF was 32 months (95% confidence interval, 23-82). Two- and 5-year overall survival were 86% and 62%, respectively, with a projected median survival of 93 months (7.75 years; 95% confidence interval, 64-177). These results show systemic therapy improved TTF and survival for patients with stage IV, no-evidence-of-disease breast cancer. Randomized studies are needed to confirm these findings and define optimal therapy.