Magrolimab in Combination With Azacitidine in Patients With Higher-Risk Myelodysplastic Syndromes: Final Results of a Phase Ib Study

PURPOSE

Magrolimab is a monoclonal antibody that blocks cluster of differentiation 47, a don't-eat-me signal overexpressed on cancer cells. Cluster of differentiation 47 blockade by magrolimab promotes macrophage-mediated phagocytosis of tumor cells and is synergistic with azacitidine, which increases expression of eat-me signals. We report final phase Ib data in patients with untreated higher-risk myelodysplastic syndromes (MDS) treated with magrolimab and azacitidine (ClinicalTrials.gov identifier: NCT03248479).

PATIENTS AND METHODS

Patients with previously untreated Revised International Prognostic Scoring System intermediate-/high-/very high-risk MDS received magrolimab intravenously as a priming dose (1 mg/kg) followed by ramp-up to a 30 mg/kg once-weekly or once-every-2-week maintenance dose. Azacitidine 75 mg/m2 was administered intravenously/subcutaneously once daily on days 1-7 of each 28-day cycle. Primary end points were safety/tolerability and complete remission (CR) rate.

RESULTS

Ninety-five patients were treated. Revised International Prognostic Scoring System risk was intermediate/high/very high in 27%, 52%, and 21%, respectively. Fifty-nine (62%) had poor-risk cytogenetics and 25 (26%) had TP53 mutation. The most common treatment-emergent adverse effects included constipation (68%), thrombocytopenia (55%), and anemia (52%). Median hemoglobin change from baseline to first postdose assessment was -0.7 g/dL (range, -3.1 to +2.4). CR rate and overall response rate were 33% and 75%, respectively. Median time to response, duration of CR, duration of overall response, and progression-free survival were 1.9, 11.1, 9.8, and 11.6 months, respectively. Median overall survival (OS) was not reached with 17.1-month follow-up. In TP53-mutant patients, 40% achieved CR with median OS of 16.3 months. Thirty-four patients (36%) had allogeneic stem-cell transplant with 77% 2-year OS.

CONCLUSION

Magrolimab + azacitidine was well tolerated with promising efficacy in patients with untreated higher-risk MDS, including those with TP53 mutations. A phase III trial of magrolimab/placebo + azacitidine is ongoing (ClinicalTrials.gov identifier: NCT04313881 [ENHANCE]).

Single-Agent Mosunetuzumab Shows Durable Complete Responses in Patients With Relapsed or Refractory B-Cell Lymphomas: Phase I Dose-Escalation Study

PURPOSE

Mosunetuzumab is a bispecific antibody targeting CD20 and CD3 that redirects T cells to engage and eliminate malignant B cells and is being developed for relapsed or refractory (R/R) B-cell non-Hodgkin lymphomas (B-NHLs).

METHODS

This first-in-human trial (ClinicalTrials.gov identifier: NCT02500407) evaluated the safety and tolerability and efficacy of mosunetuzumab in patients with R/R B-NHL and established the recommended phase II dose. Data from dose escalation are presented. Single-agent mosunetuzumab was administered intravenously in 3-week cycles, at full dose in cycle 1 day 1 (group A) or with ascending (step-up) doses during cycle 1 on days 1, 8, and 15 (group B), for eight or 17 cycles on the basis of tumor response.

RESULTS

Two hundred thirty patients were enrolled. Doses up to 2.8 mg and 60 mg were assessed in groups A and B, respectively; maximum tolerated dose was not exceeded. In group B (n = 197), common adverse events (≥ 20% of patients) were neutropenia (28.4%), cytokine release syndrome (27.4%), hypophosphatemia (23.4%), fatigue (22.8%), and diarrhea (21.8%). Cytokine release syndrome was mostly low-grade (grade ≥ 3: 1.0%) and mainly confined to cycle 1. Across the doses investigated (group B), best overall response rates were 34.9% and 66.2% in patients with aggressive and indolent B-NHL, respectively, and complete response rates were 19.4% and 48.5%. Among patients with a complete response, the median duration of response was 22.8 months (95% CI, 7.6 to not estimable) and 20.4 (95% CI, 16 to not estimable) in patients with aggressive and indolent B-NHL, respectively.

CONCLUSION

Mosunetuzumab, administered with step-up dosing, has a manageable safety profile and induces durable complete responses in R/R B-NHL. The expansion stage of the study is ongoing at the dose level of 1/2/60/60/30 mg selected for further study.

Safety and Clinical Activity of Atezolizumab in Patients with Metastatic Castration-Resistant Prostate Cancer: A Phase I Study

PURPOSE

Atezolizumab [anti-programmed death-ligand 1 (anti-PD-L1)] is well tolerated and efficacious in multiple cancers, but has not been previously evaluated in metastatic castration-resistant prostate cancer (mCRPC). This study examined the safety, efficacy, and biomarkers of atezolizumab monotherapy for mCRPC.

PATIENTS AND METHODS

This phase Ia, open-label, dose-escalation and dose-expansion study (PCD4989g) enrolled patients with mCRPC who had progressed on sipuleucel-T or enzalutamide. Atezolizumab was given intravenously every 3 weeks until confirmed disease progression or loss of clinical benefit. Prespecified endpoints included safety, efficacy, biomarker analyses, and radiographic assessments.

RESULTS

All 35 evaluable patients [median age, 68 years (range, 45-83 years)] received atezolizumab after ≥1 prior line of therapy; 62.9% of patients had received ≥3 prior lines. Treatment-related adverse events occurred in 21 patients (60.0%), with no deaths. One patient had a confirmed partial response (PR) per RECIST 1.1, and 1 patient had a PR per immune-related response criteria. The confirmed 50% PSA response rate was 8.6% (3 patients). Median overall survival (OS) was 14.7 months [95% confidence interval (CI): 5.9-not evaluable], with a 1-year OS rate of 52.3% (95% CI: 34-70); 2-year OS was 35.9% (95% CI: 13-59). Median follow-up was 13.0 months (range, 1.2-28.1 months). Biomarker analyses showed that atezolizumab activated immune responses; however, a composite biomarker failed to reveal consistent correlations with efficacy.

CONCLUSIONS

Atezolizumab was generally well tolerated in patients with mCRPC, with a safety profile consistent with other tumor types. In heavily pretreated patients, atezolizumab monotherapy demonstrated evidence of disease control; however, its limited efficacy suggests a combination approach may be needed.

Long-term Clinical Outcomes and Biomarker Analyses of Atezolizumab Therapy for Patients With Metastatic Triple-Negative Breast Cancer: A Phase 1 Study

Importance

Atezolizumab (anti-programmed cell death ligand 1 [PD-L1]) is well tolerated and clinically active in multiple cancer types. Its safety and clinical activity in metastatic triple-negative breast cancer (mTNBC) has not been reported.

Objective

To evaluate the safety, clinical activity, and biomarkers associated with the use of single-agent atezolizumab in patients with mTNBC.

Design, Setting, and Participants

Women with mTNBC (defined by investigator assessment) were enrolled between January 2013 and February 2016 in a multicohort open-label, phase 1 study at US and European academic medical centers. Median follow-up was 25.3 months (range, 0.4-45.6 months). Eligible patients regardless of line of therapy had measurable disease by Response Evaluation Criteria in Solid Tumors, version 1.1; Eastern Cooperative Oncology Group performance status of 0 to 1; and a representative tumor sample for assessment of immune cell (IC) PD-L1 expression.

Interventions

Atezolizumab was given intravenously every 3 weeks until unacceptable toxic effects or loss of clinical benefit.

Main Outcomes and Measures

Primary outcome was safety and tolerability. Activity and exploratory outcomes included objective response rate (ORR), duration of response, progression-free survival (PFS), and overall survival (OS). Outcomes were assessed in all patients and in key patient subgroups.

Results

Among 116 evaluable patients (median age, 53 years [range, 29-82 years]), treatment-related adverse events occurred in 73 (63%); 58 (79%) were grade 1 to 2. Most adverse events occurred within the first treatment year. The ORRs were numerically higher in first-line (5 of 21 [24%]) than in second-line or greater patients (6 of 94 [6%]). Median duration of response was 21 months (range, 3 to ≥38 months). Median PFS was 1.4 (95% CI, 1.3-1.6) months by RECIST and 1.9 (95% CI, 1.4-2.5) months by irRC. In first-line patients, median OS was 17.6 months (95% CI, 10.2 months to not estimable). Patients with PD-L1 expression of at least 1% tumor-infiltrating ICs had higher ORRs and longer OS (12% [11 of 91]; 10.1 [95% CI, 7.0-13.8] months, respectively) than those with less than 1% ICs (0 of 21; 6.0 [95% CI, 2.6-12.6] months, respectively). High levels of ICs (>10%) were independently associated with higher ORRs and longer OS.

Conclusions and Relevance

Single-agent atezolizumab was well tolerated and provided durable clinical benefit in patients with mTNBC with stable or responding disease and in earlier lines of treatment.

Trial Registration

ClinicalTrials.gov identifier: NCT01375842.

Association of Cancer Immunotherapy With Acute Macular Neuroretinopathy and Diffuse Retinal Venulitis

Importance

Checkpoint inhibition in cancer immunotherapy related to T-cell-driven mechanisms of action associated with acute macular neuroretinopathy (AMN) and diffuse retinal venulitis, an adverse event not previously described, is reported here.

Objective

To describe 2 patients who developed ophthalmologic events after treatment with the programmed death 1 axis inhibitor, atezolizumab.

Design, Setting, and Participants

Retrospective review of 2 patients treated with atezolizumab for metastatic breast cancer and colon cancer, respectively, who presented with AMN and diffuse retinal venulitis conducted at 2 tertiary medical centers.

Main Outcomes and Measures

Multimodal imaging including near infrared, optical coherence tomography, and fluorescein angiography were used to characterize retinal vascular abnormalities.

Results

Based on optical coherence tomography and multimodal imaging findings, the clinical diagnosis of AMN associated with diffuse retinal venulitis was made in these 2 patients receiving atezolizumab.

Conclusions and Relevance

While only 2 cases of patients receiving the programmed death ligand 1 inhibitor atezolizumab who experienced AMN and diffuse retinal venulitis are described here, these findings suggest that patients receiving programmed death 1 axis inhibitor therapies may need to be monitored for unexpected immune-related ocular toxicity including abnormalities of the microvasculature and large retinal vessels. Further studies might investigate the potential mechanisms of retinal vascular changes associated with these therapies.

Tumor immune microenvironment and genomic evolution in a patient with metastatic triple negative breast cancer and a complete response to atezolizumab

BACKGROUND

Metastatic TNBC (mTNBC) has a poor prognosis and few treatment options. The anti-PD-L1 antibody atezolizumab demonstrated clinical activity in mTNBC patients with PD-L1-positive tumor-infiltrating immune cells. The current study describes the tumor immune microenvironment (TiME) and genomic evolution across sequential therapies in a patient with a 31-year history of TNBC and a complete response (CR) to atezolizumab monotherapy.

MATERIALS AND METHODS

In 1986, the patient had surgery and radiotherapy (XRT) for newly diagnosed TNBC, followed by surgery and adjuvant chemotherapy for two locoregional recurrences. She developed mTNBC in 2009 and was sequentially treated with capecitabine, gemcitabine-carboplatin-iniparib (GCI), XRT and an experimental vaccine. She experienced disease progression (PD) to all these therapies. In 2013, she had a PD-L1 positive tumor and enrolled in a phase 1 atezolizumab monotherapy study (PCD4989g; NCT01375842). She received atezolizumab for 1 year with initial pseudo-progression followed by a partial response. After 1 year without treatment she experienced PD, reinitiated atezolizumab and subsequently achieved CR. Tumor specimens were collected at numerous times between 2008 and 2015 and assessed by immunohistochemistry, RNA-seq and DNA-seq.

RESULTS

TiME biomarkers, including CD8, ICs and PD-L1 on IC, increased after capecitabine and remained high after GCI, XRT and through pseudo-progression on atezolizumab. At PD post-atezolizumab exposure, TiME biomarkers decreased but PD-L1 status remained positive. Immune-related RNA signatures confirmed these findings. TNBC subtyping revealed evolution from luminal androgen receptor (LAR) to basal-like immune activated (BLIA). Genomic profiling showed truncal alterations in RB1 and TP53, while the presence of other genomic alterations varied over time. Tumor mutational burden peaked after XRT and declined after atezolizumab exposure.

CONCLUSIONS

This case report describes the evolution of TiME and TNBC molecular subtypes/genomics over time with sequential therapies in a TNBC patient with a CR to atezolizumab monotherapy. These data suggest the TiME is pliable and may be manipulated to maximize response to immunotherapy (NCT01375842, https://clinicaltrials.gov/ct2/show/NCT01375842?term=NCT01375842&rank=1 ).

Atezolizumab (MPDL3280A) Monotherapy for Patients With Metastatic Urothelial Cancer: Long-term Outcomes From a Phase 1 Study

Importance

Atezolizumab (anti-programmed death ligand 1) has demonstrated safety and activity in advanced and metastatic urothelial carcinoma, but its long-term clinical profile remains unknown.

Objective

To report long-term clinical outcomes with atezolizumab therapy for patients with metastatic urothelial carcinoma.

Design, Setting, and Participants

Patients were enrolled in an expansion cohort of an ongoing, open-label, phase 1 study. Median follow-up was 37.8 months (range, >0.7 to 44.4 months). Enrollment occurred between March 2013 and August 2015 at US and European academic medical centers. Eligible patients had measurable disease per Response Evaluation Criteria in Solid Tumors version 1.1, Eastern Cooperative Oncology Group performance status 0 to 1, and a representative tumor sample. Programmed death ligand 1 expression on immune cells was assessed (VENTANA SP142 assay).

Interventions

Atezolizumab was given intravenously every 3 weeks until unacceptable toxic effects, protocol nonadherence, or loss of clinical benefit.

Main Outcomes and Measures

Primary outcome was safety. Secondary outcomes included objective response rate, duration of response, and progression-free survival. Response and overall survival were assessed in key baseline subgroups.

Results

Ninety-five patients were evaluable (72 [76%] male; median age, 66 years [range, 36-89 years]). Forty-five (47%) received atezolizumab as third-line therapy or greater. Nine patients (9%) had a grade 3 to 4 treatment-related adverse event, mostly within the first treatment year; no serious related adverse events were observed thereafter. One patient (1%) discontinued treatment due to a related event. No treatment-related deaths occurred. Responses occurred in 26% (95% CI, 18%-36%) of patients. Median duration of response was 22.1 months (range, 2.8 to >41.0 months), and median progression-free survival was 2.7 months (95% CI, 1.4-4.3 months). Median overall survival was 10.1 months (95% CI, 7.3-17.0 months); 3-year OS rate was 27% (95% CI, 17%-36%). Response occurred in 40% (95% CI, 26%-55%; n = 40) and 11% (95% CI, 4%-25%; n = 44) of patients with programmed death ligand 1 expression of at least 5% tumor-infiltrating immune cells (IC2/3) or less than 5% (IC0/1), respectively. Median overall survival in patients with IC2/3 and IC0/1 was 14.6 months (95% CI, 9.0 months to not estimable) and 7.6 months (95% CI, 4.7 to 13.9 months), respectively.

Conclusions and Relevance

Atezolizumab remained well tolerated and provided durable clinical benefit to a heavily pretreated metastatic urothelial carcinoma population in this long-term study.

Trial Registration

clinicaltrials.gov Identifier: NCT01375842.

Safety, clinical activity and biomarker assessments of atezolizumab from a Phase I study in advanced/recurrent ovarian and uterine cancers

OBJECTIVE

Patients with advanced/recurrent epithelial ovarian and uterine cancers have limited treatment options beyond platinum chemotherapy. Both tumor types can express programmed death-ligand 1 (PD-L1), providing a potential therapeutic target for these patients. Here we present data from the ovarian and uterine cancer cohorts of the Phase I atezolizumab monotherapy study (PCD4989g).

METHODS

This Phase I, multi-center, first-in-human, open-label, dose-escalation/expansion clinical trial investigated single-agent atezolizumab in cohorts of patients with recurrent epithelial ovarian or uterine cancer. The primary objective was to evaluate the safety and tolerability of single-agent atezolizumab. Anti-tumor activity and preliminary assessment of potential biomarkers were evaluated as secondary and exploratory objectives, respectively.

RESULTS

The ovarian and uterine cancer cohorts enrolled 12 and 15 patients, respectively (10 [83%] and 5 [33%], respectively, had PD-L1 ≥ 5% on tumor-infiltrating immune cells). Atezolizumab was generally well tolerated with no new safety signals identified. The safety profiles in both cohorts were consistent with the known profile of atezolizumab monotherapy. Treatment-related adverse events (AEs) were mostly Grade ≤ 2, with no treatment-related Grade ≥ 4 AEs reported. Preliminary anti-tumor activity, with long durations of response, was observed in 2 patients from each cohort (ovarian cancer, 8.1 and 30.6+ months; uterine cancer, 7.3 and 16.6+ months). High microsatellite instability and tumor mutational burden were noted in the responders from the uterine cancer cohort.

CONCLUSIONS

Atezolizumab monotherapy was well tolerated in patients with epithelial ovarian or uterine cancer and may have clinical activity warranting further investigation.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01375842.

Abstract OT2-06-04: MORPHEUS: A phase Ib/II trial platform evaluating the safety and efficacy of multiple cancer immunotherapy combinations in patients with hormone receptor–positive and triple-negative breast cancer

Background:

Cancer immunotherapy (CIT) has significantly improved overall survival across multiple tumor types, but only subsets of patients experience durable response with single-agent CIT. Combinations of CIT with targeted therapy or chemotherapy may be needed in order to target multiple cancer immune escape mechanisms simultaneously, thus providing personalized treatment options that extend clinical benefit to more patients. The MORPHEUS platform includes multiple phase Ib/II trials designed to identify early signals of safety and activity of CIT combinations. Using a randomized trial design, multiple CIT combination arms are compared with a single standard-of-care control arm. These trials have the flexibility to open new treatment arms with novel CIT combinations as they become available and to close arms that show minimal activity or unacceptable toxicity. Here we describe MORPHEUS trials in patients with metastatic or unresectable locally advanced hormone receptor–positive (HR+BC) or triple-negative breast cancer (TNBC), 2 patient populations in need of more treatment options.

Trial design:

MORPHEUS-HR+BC (NCT03280563) will enroll patients with metastatic or unresectable locally advanced HR+BC who have progressed during or after first-line treatment with a cyclin-dependent kinase (CDK) 4/6 inhibitor and whose tumors do not express human epidermal growth factor 2 (HER2). MORPHEUS-TNBC (NCT03424005) will enroll patients with metastatic or unresectable locally advanced TNBC who have progressed during or after first-line treatment with chemotherapy. For both studies, key inclusion criteria include Eastern Cooperative Oncology Group performance status of 0-1 (stage 1) or 0-2 (stage 2) and measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Key exclusion criteria include prior treatment with T-cell co-stimulating or immune checkpoint blockade therapies, and symptomatic, untreated, or actively progressing central nervous system metastases. Patients in both trials will be randomized to one of the CIT atezolizumab combination arms or a control arm (up to 5 arms in HR+BC and up to 6 arms in TNBC). Patients experiencing loss of clinical benefit or unacceptable toxicity in stage 1 may be eligible to switch to a different CIT atezolizumab combination arm in stage 2. Primary endpoints are safety measures and investigator-assessed objective response rate per RECIST v1.1. Progression-free survival, overall survival, duration of response, clinical benefit rate (HR+BC) or disease control rate (TNBC) are among the secondary endpoints. Exploratory biomarkers will also be examined.

Citation Format: Yardley DA, Abu-Khalaf M, Boni V, Brufsky A, Emens LA, Gutierrez M, Hurvitz S, Im S-A, Loi S, McCune SL, Schmid P, O'Hear C, Zhang X, Vidal GA. MORPHEUS: A phase Ib/II trial platform evaluating the safety and efficacy of multiple cancer immunotherapy combinations in patients with hormone receptor–positive and triple-negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT2-06-04.

Safety and clinical activity of atezolizumab monotherapy in metastatic non-small-cell lung cancer: final results from a phase I study

INTRODUCTION

Atezolizumab, an anti-programmed death-ligand 1 (PD-L1) antibody, inhibits PD-L1:PD-1 and PD-L1:B7.1 interactions, restoring anticancer immunity. Here, we report final analyses from the non-small-cell lung cancer (NSCLC) cohort of the first atezolizumab phase I study.

METHODS

Patients with NSCLC received atezolizumab 1-20 mg/kg or 1200 mg intravenously every 3 weeks. Baseline PD-L1 expression on tumour cells (TCs) and tumour-infiltrating immune cells (ICs) was assessed (VENTANA SP142 immunohistochemistry assay). Exploratory subgroup analyses investigated responses by baseline PD-L1 expression and oncogenic mutational status.

RESULTS

Eighty-nine patients, 98% of whom had received previous systemic therapy, were evaluable for safety and antitumour activity. Atezolizumab was well tolerated, with grade III/IV treatment-related adverse events (TRAEs) observed in 10 patients (11%). All-grade TRAEs occurring in >10% of patients were fatigue, nausea and decreased appetite; grade III/IV TRAEs occurring in >2% of patients were fatigue, dyspnoea, hyponatremia and hypoxia. One patient died from treatment-unrelated pneumonia. Objective response rate (ORR) was 50% (95% confidence interval [CI], 28%-72%), 33% (20%-48%), 29% (18%-41%) and 11% (1%-35%) for the TC3 or IC3, TC2/3 or IC2/3, TC1/2/3 or IC1/2/3 and TC0 and IC0 subgroups, respectively. All-patient ORR was 23% (95% CI, 14%-33%). Median duration of response was 16.4 months (range, 7.2-53.4+). One-, 2-, and 3-year survival rates were 63% (95% CI, 53%-73%), 37% (26%-47%) and 28% (18%-38%), respectively.

CONCLUSIONS

Single-agent atezolizumab was well tolerated with long-term clinical benefits, including durable responses and survival, in pretreated NSCLC. Improved responses and survival rates were seen with increasing baseline PD-L1 expression. CLINICALTRIALS.

GOV IDENTIFIER

NCT01375842.

Abstract 2616: Baseline blood lymphocytes are associated with improved clinical outcome in atezolizumab-treated patients across multiple indications

Background: The PD-L1/PD-1 inhibitors activate the immune system both in the tumor microenvironment and peripheral blood. Here we investigated the relationship between peripheral immune system and clinical outcome of metastatic cancer patients treated with atezolizumab (anti-PDL1) across five tumor types.

Methods: 426 patients with melanoma (n=45), non-small cell lung cancer (NSCLC, n=89), kidney cancer (RCC, n=72), triple-negative breast cancer (TNBC, n=116) and bladder cancer (UBC, n=104) were treated with atezolizumab in the phase I clinical trial PCD4989g (NCT01375842). Normal/abnormal blood neutrophils, monocytes, eosinophils, basophils and lymphocytes were measured by local laboratories, while T (CD3, CD4 and CD8), B (CD19), and NK (CD56) lymphocyte subsets were centrally analyzed by flow cytometry. Neutrophil:lymphocyte ratio (NLR) and relative lymphocyte counts (RLC) were also evaluated. Association of the immune cell subsets and clinical outcome (ORR, PFS and OS) was assessed in multivariate analyses considering liver metastases, LDH, line of therapy and ECOG performance status.

Results: The prevalence of hematologic abnormalities across tumors was: lymphopenia (27-57%), followed by neutrophilia (2-24%), monocytosis (0-15%), eosinophilia (1-13%), eosinopenia (0-14%), basophilia (2-7%) and basopenia (0-6%). Neutrophilia, monocytosis, lymphopenia and low/high eosinophils were associated with worse PFS and OS, although with a different imprint depending on tumor ontogeny: neutrophilia was linked to reduced OS in melanoma and PFS for UBC, monocytosis was associated with lower OS in TNBC and UBC. Lymphopenia was associated with reduced PFS and OS in NSCLC, TNBC and reduced PFS in melanoma. NLR>=5 was associated with reduced PFS in melanoma, NSCLC, RCC, UBC and reduced OS in UBC, NSCLC and TNBC. RLC>=17.5% was linked to longer PFS in melanoma, RCC, UBC and to increased OS in TNBC, NSCLC and UBC. Lymphocyte subset analysis showed lymphopenia in B cells (40-61%), CD3 T cells (32-71%), CD4 T cells (28-66%), CD8 T cells (25-46%) and NK cells (16-23%). CD3 lymphopenia was associated to reduced OS in NSCLC, and CD4 lymphopenia was associated to reduced OS in NSCLC and TNBC. NK lymphopenia was associated to decreased OS and PFS in TNBC.

Conclusion: This is the first study showing that higher pretreatment relative lymphocyte counts is associated to improved clinical outcome in patients from different tumor etiologies treated with atezolizumab. The association of peripheral T cell counts to improved outcome in some indications suggests that the local antitumor response may be linked to pre-existing systemic T cells.

Citation Format: Yijin Li, Ching-Wei Chang, Marcella Fasso, Carol O'Hear, Priti S. Hegde, Luciana Molinero. Baseline blood lymphocytes are associated with improved clinical outcome in atezolizumab-treated patients across multiple indications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2616.

A phase Ia study of safety and clinical activity of atezolizumab (atezo) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

187

Background: In the past decade, several therapies have been approved for mCRPC. However, most pts develop resistance and experience disease progression. Thus, there remains a high unmet need. Atezo (anti–PD-L1) blocks the interaction between PD-L1 and its receptors, PD-1 and B7.1, thereby restoring anti-tumor immunity. Atezo has demonstrated clinical efficacy in many tumor types. Here we report the clinical safety and activity of atezo in pts with mCRPC from a Phase Ia study (PCD4989g; NCT01375842). Methods: Eligible pts previously received enzalutamide and/or sipuleucel-T for mCRPC. Pts also had PSA or radiographic progression prior to enrollment. Atezo 1200mg was administered IV q3w. CT and bone scans were performed q6w for 24w and q12w thereafter (q6w if treatment beyond disease progression). Primary objectives were safety and tolerability; OS was an exploratory objective. mCRPC cohort–specific objectives included PSA response, radiographic progression per PCWG2 criteria, soft tissue response per RECIST v1.1 and immune-related response criteria (irRC). Survival follow-up data was collected ≈ every 3 mo until death or loss to follow-up. Results: The 15 pts in the initial mCRPC cohort were evaluated (clinical cutoff: December 31, 2016). 13 pts (87%) had received ≥ 2 prior lines of therapy for mCRPC. Median survival follow-up was 15.8 mo (range, 2.3-23.0). 9 pts (60%) had a treatment-related AE (TRAE); only 1 pt (7%) experienced a Gr 3 TRAE (hyponatremia). No Gr 4-5 TRAEs were reported. The landmark 12-mo OS rate was 55.6% (95% CI: 27.4, 83.7); median OS was not reached (range, 2.3-23.0 mo). Median PFS was 3.4 mo (95% CI: 2.3, 5.7); the 6-mo PFS rate was 26.7% (95% CI: 4.3, 49.1). 1 pt (9%) had a PR per irRC (irPR); 5 pts (45%) had SD per RECIST v1.1 and irRC. 2 pts (13%) had a ≥ 50% decrease in PSA from baseline. The pt who experienced an irPR had increased CD8 expression and expansion of T-cell clones on study treatment. Conclusions: Atezo was well tolerated and demonstrated long-term disease control in pts with heavily pretreated mCRPC, with a 12-mo OS rate of 55.6%. Preliminary biomarker analyses from the pt who experienced an irPR were suggestive of an activated immune response. Clinical trial information: NCT01375842.

Clinical activity, safety and biomarker results from a phase Ia study of atezolizumab (atezo) in advanced/recurrent endometrial cancer (rEC)

5585

Background: The prognosis for patients (pts) with rEC remains poor, with a 5-y OS of 20%-26%. We report safety, clinical activity and biomarker data from a Phase Ia study of atezo (anti–PD-L1) monotherapy in rEC. Methods: Atezo 1200 mg or 15 mg/kg IV q3w was administered until toxicity or loss of clinical benefit. Pts were initially eligible based on PD-L1 status ( > 5% of tumor-infiltrating immune cells [IC; IC2/3], VENTANA SP142 IHC assay) and then enrolled regardless of PD-L1 status. Tumor-infiltrating lymphocytes (TILs) were assessed by H&E. The FoundationOne NGS panel was used for microsatellite instability (MSI) and tumor mutation load analyses. Confirmed ORR and PFS were assessed by RECIST v1.1. Results: As of March 31, 2016, 15 pts were evaluable for safety and efficacy (minimum follow-up, 11.2 mo). The median age was 61 y (range, 20-74 y), 53% were ECOG PS 1 and 93% had ≥ 2 prior systemic therapies; 10 (67%) pts had prior RT. Pts were MSI-H (1/15), MSS (7/15) or MSI unknown (7/15). EC subtypes were endometrioid (5/15), serous (5/15), ER+ leiomyosarcoma (1/15) or unknown (4/15). Five (33%) pts were IC2/3, and 10 (67%) pts were IC0/1. Seven (47%) pts had any related AE, mainly G1-2 (5 pts). No G4-5 related AEs occurred. Two pts had related SAEs (colitis; rash). ORR was 13% (2/15) by RECIST. Both pts achieved PR and were IC2/3. ORR for IC2/3 pts was 40% (2/5). One responder was MSS and heavily infiltrated with TILs (IC3, 70% TILs, 1.8 Mut/Mb, unknown subtype); the other responder was hypermutated, MSI-H and moderately infiltrated with TILs (IC2, 10% TILs, 237 Mut/Mb, endometrioid). DOR in the 2 responders was 7.3 and 8.1+ mo. mPFS was 1.7 mo (range, 0.6-11+ mo); mOS was 9.6 mo (range, 0.6-11.8+ mo). Of the remaining pts, 2 had SD, 9 had PD and 2 were non-evaluable. DCR (PR + SD) was 27%. A trend for higher PFS and OS was seen in IC2/3 vs IC0/1 pts. Conclusions: Atezo had a favorable safety profile in rEC, with durable clinical benefit in some pts. Clinical benefit appeared to increase with higher PD-L1 expression, suggesting a link between PD-L1 status and response. Hypermutation and/or high immune infiltration may be linked to response to PD-L1 blockade, and further evaluation is merited. Clinical trial information: NCT01375842.

Atezolizumab (atezo) in patients with metastatic urothelial carcinoma (mUC): A 2-year clinical update from a phase Ia study

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Background: Atezo (anti–PD-L1) has demonstrated safety and efficacy in a broad range of cancers and is approved in the United States for mUC previously treated with platinum-based chemotherapy. Here we report long-term results in mUC from Phase Ia study NCT01375842 (PCD4989g). Methods: Previously treated mUC patients received atezo 15 mg/kg or 1200 mg IV q3w. Enrollment in this Phase Ia expansion cohort initially required PD-L1–selected status and later opened to patients regardless of PD-L1 expression on tumor-infiltrating immune cells. The primary endpoint was safety/tolerability. Secondary endpoints included investigator-assessed RECIST v1.1 ORR (confirmed), DOR and OS. Results: 95 patients were safety evaluable (Table). Median age was 66 years, 76% were male and 80% had primary bladder tumors. 61% had ECOG PS 1. 52% received ≥ 3 prior systemic therapies for mUC (70% platinum). Median treatment duration was 3 months (range: 0-32 months); 24% were treated for ≥ 1 year. Treatment-related AEs occurred in 66% (all Grade) and 8% (Grade 3-4) of patients. No treatment-related deaths were reported. In 94 objective response–evaluable patients (follow-up ≥ 12 weeks), the ORR was 27% (95% CI: 18, 37%), and the CR rate was 10%; the SD rate was 19%. mDOR was 22.1 months (95% CI: 12.1, NE months) in all patients; 56% of responses (7/9 CRs and 7/16 PRs) were ongoing at the December 15, 2015 data cutoff. With a 24-month median follow-up duration (range: 1+ to 32 months), the 1-year OS rate was 47% (95% CI: 36, 58%), and the 2-year rate was 29% (19, 40%); mOS is in the Table. Updated clinical data with further follow-up and analyses by PD-L1 status will be presented. Conclusions: Long-term treatment with atezo was well tolerated, without new safety signals in heavily pre-treated mUC patients. The durability of responses, including CRs, along with extended OS, confirm atezo as a new standard for previously treated mUC patients. Clinical trial information: NCT01375842. [Table: see text]

Anti-CD33 chimeric antigen receptor targeting of acute myeloid leukemia

Current therapies for acute myeloid leukemia are associated with high failure and relapse rates. Adoptive immunotherapies, which have shown promise in the treatment of hematologic malignancies, have the potential to target acute myeloid leukemia through pathways that are distinct and complementary to current approaches. Here, we describe the development of a novel adoptive immunotherapy specific for this disease. We generated a second generation CD33-specific chimeric antigen receptor capable of redirecting cytolytic effector T cells against leukemic cells. CD33 is expressed in approximately 90% of acute myeloid leukemia cases and has demonstrated utility as a target of therapeutic antibodies. Chimeric antigen receptor-modified T cells efficiently killed leukemia cell lines and primary tumor cells in vitro. The anti-leukemia effect was CD33-specific, mediated through T-cell effector functions, and displayed tumor lysis at effector:target ratios as low as 1:20. Furthermore, the CD33-redirected T cells were effective in vivo, preventing the development of leukemia after prophylactic administration and delaying the progression of established disease in mice. These data provide pre-clinical validation of the effectiveness of a second-generation anti-CD33 chimeric antigen receptor therapy for acute myeloid leukemia, and support its continued development as a clinical therapeutic.

Gemtuzumab ozogamicin can reduce minimal residual disease in patients with childhood acute myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is an active agent for the treatment of CD33-postive acute myeloid leukemia (AML) and may improve the outcome of specific patient subgroups when combined with conventional chemotherapy. However, to the best of the authors' knowledge, the effects of GO on levels of minimal residual disease (MRD) are unknown.

METHODS

Pediatric patients with AML who received GO, either alone or in combination with chemotherapy on the AML02 multicenter trial, were analyzed to determine the effects of GO on MRD and outcome.

RESULTS

Among 17 patients who received GO alone because of persistent leukemia, 14 had a reduction in their MRD level and 13 became MRD negative. Of the 29 who received chemotherapy in combination with GO after responding poorly to chemotherapy, 28 demonstrated reduced MRD and 13 became MRD negative. Treatment with GO effectively reduced MRD before hematopoietic stem cell transplantation and was not found to be associated with increased treatment-related mortality after transplantation.

CONCLUSIONS

GO is effective in reducing MRD levels in pediatric patients with AML and may improve the outcome of those patients at high risk of disease recurrence.

Antibody buffering of systemically administered lysozyme

OBJECTIVE

To assess the ability of an anti-lysozyme antibody to stabilize the plasma pharmacokinetics of lysozyme through a 'buffering' effect.

METHODS

Hen egg lysozyme was radiolabeled with (14)C and infused with or without the murine anti-lysozyme antibody D1.3 into the jugular vein of rats. The dosages of antibody and lysozyme were varied, and the antibody and lysozyme were administered either together or in separate infusions.

RESULTS

Buffering of lysozyme with an equimolar amount of D1.3 more than doubled the plasma half-life of lysozyme and addition of more antibody buffer prolonged the half-life to an even greater extent. D1.3 bound lysozyme that was infused several minutes after the D1.3 administration, indicating that D1.3 can be charged with drug in vivo.

CONCLUSION

Antibody buffering of monovalent therapeutic enzymes is possible and may have potential for clinical use.

Antibody buffering in the brain

The efficacy of chemotherapy on brain tumors is often hindered by the presence of the blood brain barrier. This barrier keeps many systemically administered substances from entering the cerebrospinal fluid (CSF), while allowing intrathecally administered drugs free passage out of that compartment. Therefore, achieving a therapeutic concentration of a cell cycle inhibitor in the CSF for a time long enough to have a cytotoxic effect on slow-growing tumor cells has proven difficult. The ability of an antibody to prolong ligand half-life and bioactivity has been previously described occurring in the plasma. This phenomenon has not yet been described or exploited for use in the CSF compartment. Antibodies often have a longer residence time in the CSF than small-molecule drugs, so antibody buffering, administration of a drug with its specific antibody, can prolong the bioactive lifetime of a drug in the CSF. Here we describe antibody buffering of the small molecule hapten 2-phenyl-oxazol-5-one-methylene-gamma-amino butyrate in the CSF of a rats. Not only does the presence of an antibody buffer increase the half-life of both total and free hapten in the CSF, but the antibody can be re-charged in situ with fresh hapten, even days after the initial antibody infusion. Antibody buffering may provide a viable option for delivering a stable, bio-available concentration of a drug that is normally rapidly eliminated from the CSF.