BACKGROUND: BPDCN is a rare, aggressive hematologic malignancy characterized by historically poor overall survival and limited therapeutic options. Despite the recent approval of tagraxofusp-erzs for BPDCN, outcomes remain suboptimal for many patients. Additionally, patients with BPDCN are older and often have co-morbidities at baseline, preventing them from receiving tagraxofusp-erzs. Therefore, novel therapies are needed in the frontline setting for patients with BPDCN. Overexpression of CD123 (IL-3Rα) is present in all BPDCN cases, thereby establishing this surface marker as a target for therapeutic intervention. IMGN632 is a CD123-targeting ADC, comprised of a high-affinity anti-CD123 antibody coupled to a DNA-alkylating payload of the novel IGN (indolinobenzodiazepine pseudodimer) class. IMGN632 has demonstrated favorable safety and promising clinical activity in relapsed/refractory (R/R) BPDCN [Blood (2020) 136 (Supplement 1): 11-13], leading to the FDA granting IMGN632 Breakthrough Therapy Designation (BTD) for R/R BPDCN (Oct 2020).

Following BTD and alignment with FDA, a pivotal cohort in frontline (no prior systemic treatment) BPDCN patients was initiated in addition to a continuing cohort of patients with R/R disease, where we have enrolled 33 patients to date. Here we report the initial experience of three frontline patients who are not part of the pivotal cohort.

METHODS: IMGN632 was administered IV at a dose of 0.045 mg/kg on day 1 of a 21-day cycle to all patients. Efficacy was assessed using modified Severity Weighted Assessment Tool (for skin lesions), PET/CT, and blast percentage in bone marrow aspirates. The response criteria were adapted from established BPDCN criteria (Pemmaraju NEJM 2019).

RESULTS: Three patients with frontline BPDCN (no prior systemic therapy) received IMGN632. All three of these frontline patients achieved a clinical complete remission (CRc).

Patient 1 was a 79yo woman who presented with skin, nodal, and extensive bone marrow disease (80% involvement). After one dose of IMGN632, she cleared her bone marrow (0%), and after 3 cycles, her nodal lesions and skin lesions resolved to achieve a CRc. Upon complete response, treatment was held due to patient co-morbidities. With just 3 cycles of IMGN632, this patient achieved duration of response (DOR) of 10.7 months without further therapy. Patient 2 was a 67yo man who had extensive skin disease covering >20% of the body; over several cycles, he achieved a PR then a CRc and bridged to an allogeneic stem cell transplant (SCT). The patient achieved a DOR of 13.5 months, with no evidence of disease relapse when he died from graft versus host disease. Patient 3 was a 66yo woman who presented with extensive skin and nodal lesions. After improvement over 4 cycles, she achieved a CRc with clearing of most of her skin lesions and all nodal lesions. Unfortunately, while still in CRc, the patient died of COVID-19 pneumonia, with a DOR of 3.7 months.

CONCLUSION: Administration of IMGN632 to frontline BPDCN patients resulted in clinical complete remission in the initial three patients with durable responses in the two non-COVID impacted patients. None of these patients progressed while on therapy, and one patient successfully bridged to SCT. Enrollment continues in the pivotal frontline and R/R cohorts. (BPDCNtrial.com; NCT03386513).

Disclosures

Pemmaraju: Sager Strong Foundation: Other; Daiichi Sankyo, Inc.: Other, Research Funding; Aptitude Health: Consultancy; ASH Communications Committee: Membership on an entity's Board of Directors or advisory committees; Affymetrix: Consultancy, Research Funding; HemOnc Times/Oncology Times: Membership on an entity's Board of Directors or advisory committees; ASCO Leukemia Advisory Panel: Membership on an entity's Board of Directors or advisory committees; Dan's House of Hope: Membership on an entity's Board of Directors or advisory committees; Samus: Other, Research Funding; Springer Science + Business Media: Other; DAVA Oncology: Consultancy; Plexxicon: Other, Research Funding; Cellectis S.A. ADR: Other, Research Funding; Protagonist Therapeutics, Inc.: Consultancy; CareDx, Inc.: Consultancy; Novartis Pharmaceuticals: Consultancy, Other: Research Support, Research Funding; Clearview Healthcare Partners: Consultancy; Blueprint Medicines: Consultancy; Incyte: Consultancy; LFB Biotechnologies: Consultancy; Roche Diagnostics: Consultancy; MustangBio: Consultancy, Other; Abbvie Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Celgene Corporation: Consultancy; Stemline Therapeutics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Bristol-Myers Squibb Co.: Consultancy; ImmunoGen, Inc: Consultancy; Pacylex Pharmaceuticals: Consultancy. Martinelli: Incyte: Consultancy; Daichii Sankyo: Consultancy; Jazz Pharmaceuticals: Consultancy; Astellas: Consultancy, Speakers Bureau; Abbvie: Consultancy; Roche: Consultancy; Pfizer: Consultancy, Speakers Bureau; Stemline Therapeutics: Consultancy; Celgene /BMS: Consultancy, Speakers Bureau. Lane: Qiagen: Consultancy, Honoraria; N-of-One: Consultancy, Honoraria; Stemline Therapeutics: Research Funding; AbbVie: Research Funding. Deconinck: Imunogen: Membership on an entity's Board of Directors or advisory committees; Stemline Therapetutics: Membership on an entity's Board of Directors or advisory committees; Chugai: Research Funding; Novartis: Research Funding; Pfizer: Other: Travel Grants, Research Funding; Abbevie: Research Funding. Wang: Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; Kite Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Other: Advisory Board; Kura Oncology: Consultancy, Honoraria, Other: Advisory board, steering committee, Speakers Bureau; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Honoraria, Other: Advisory Board; Genentech: Membership on an entity's Board of Directors or advisory committees; Mana Therapeutics: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Other: Advisory Board, Speakers Bureau; Stemline Therapeutics: Consultancy, Honoraria, Other: Advisory board, Speakers Bureau; Takeda: Consultancy, Honoraria, Other: Advisory board; DAVA Oncology: Consultancy, Speakers Bureau; Rafael Pharmaceuticals: Other: Data safety monitoring committee; Gilead: Consultancy, Honoraria, Other: Advisory board; Daiichi Sankyo: Consultancy, Honoraria, Other: Advisory board; PTC Therapeutics: Consultancy, Honoraria, Other: Advisory board; Genentech: Consultancy; MacroGenics: Consultancy. Sweet: Bristol Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rizzieri: AbbVie: Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Teva: Membership on an entity's Board of Directors or advisory committees; Acrotech: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kite: Honoraria, Speakers Bureau; Karyopharm: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees; Celltrion: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Mustang: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Honoraria; Pharmacyclics: Honoraria. DeAngelo: Shire: Consultancy; Takeda: Consultancy; Abbvie: Research Funding; Novartis: Consultancy, Research Funding; GlycoMimetics: Research Funding; Agios: Consultancy; Blueprint Medicines Corporation: Consultancy; Amgen: Consultancy; Pfizer: Consultancy; Incyte Corporation: Consultancy; Jazz: Consultancy; Forty-Seven: Consultancy; Autolus: Consultancy. Montesinos: Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Forma Therapeutics: Consultancy; Stemline/Menarini: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Glycomimetics: Consultancy; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Tolero Pharmaceutical: Consultancy; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Erba: AbbVie Inc; Agios Pharmaceuticals Inc; Astellas; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Daiichi Sankyo Inc; Genentech, a member of the Roche Group; GlycoMimetics Inc; Incyte Corporation; Jazz Pharmaceuticals Inc; Kura Oncology; Nov: Other: Advisory Committee; AbbVie Inc; Agios Pharmaceuticals Inc; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Incyte Corporation; Jazz Pharmaceuticals Inc; Novartis: Speakers Bureau; AbbVie Inc: Other: Independent review committee; AbbVie Inc; Agios Pharmaceuticals Inc; ALX Oncology; Amgen Inc; Daiichi Sankyo Inc; FORMA Therapeutics; Forty Seven Inc; Gilead Sciences Inc; GlycoMimetics Inc; ImmunoGen Inc; Jazz Pharmaceuticals Inc; MacroGenics Inc; Novartis; PTC Therapeutics: Research Funding. Konopleva: Ascentage: Other: grant support, Research Funding; Sanofi: Other: grant support, Research Funding; Stemline Therapeutics: Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; KisoJi: Research Funding; Rafael Pharmaceuticals: Other: grant support, Research Funding; AstraZeneca: Other: grant support, Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Calithera: Other: grant support, Research Funding; Cellectis: Other: grant support; Ablynx: Other: grant support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support. Kantarjian: Novartis: Honoraria, Research Funding; Jazz: Research Funding; Daiichi-Sankyo: Research Funding; Pfizer: Honoraria, Research Funding; KAHR Medical Ltd: Honoraria; Astellas Health: Honoraria; Astra Zeneca: Honoraria; NOVA Research: Honoraria; Aptitude Health: Honoraria; Immunogen: Research Funding; Ipsen Pharmaceuticals: Honoraria; BMS: Research Funding; Ascentage: Research Funding; Amgen: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Precision Biosciences: Honoraria; Taiho Pharmaceutical Canada: Honoraria. Walter: Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Amgen, Inc.: Consultancy, Research Funding; Amphivena Therapeutics, Inc.: Current equity holder in publicly-traded company; Aptevo Therapeutics, Inc.: Consultancy, Research Funding; Arog Pharmaceuticals, Inc.: Research Funding; Astellas Pharma US, Inc.: Consultancy; BioLineRx, Ltd.: Consultancy, Research Funding; Boston Biomedical, Inc.: Consultancy; Bristol Myers Squibb, Inc.: Consultancy; Celgene, Inc.: Consultancy, Research Funding; Genentech, Inc.: Consultancy; GlaxoSmithKline, Inc.: Consultancy; ImmunoGen, Inc.: Research Funding; Janssen Global Services, LLC: Consultancy; Janssen Research & Development, Inc.: Research Funding; Jazz Pharmaceuticals, Inc.: Consultancy, Research Funding; Kite Pharma, Inc.: Consultancy; Kronos Bio, Inc.: Consultancy; Kura Oncology, Inc.: Research Funding; Macrogenics, Inc.: Research Funding; New Link Genetics: Consultancy; Pfizer, Inc.: Consultancy, Research Funding; Race Oncology Ltd.: Consultancy; Selvita: Research Funding; Stemline Therapeutics, Inc.: Research Funding. Aribi: Seagen: Consultancy. Levy: Beigene: Consultancy, Honoraria, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; TG Therapeutics: Consultancy, Honoraria, Speakers Bureau; Gilead Sciences, Inc.: Consultancy, Honoraria, Speakers Bureau; Janssen Pharmaceuticals: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Morphosys: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Dova: Consultancy, Other: Promotional speaker; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; GSK: Consultancy, Other: Promotional speaker; Karyopharm: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Epizyme: Consultancy, Other: Promotional speaker; Takeda: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Amgen Inc.: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; AbbVie: Consultancy, Honoraria, Other: Promotional speaker, Speakers Bureau; Novartis: Consultancy, Other: Promotional speaker. Malcolm: Immunogen: Current Employment. Zweidler-McKay: ImmunoGen: Current Employment. Daver: Astellas: Consultancy, Research Funding; Trovagene: Consultancy, Research Funding; Sevier: Consultancy, Research Funding; Novartis: Consultancy; Bristol Myers Squibb: Consultancy, Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Novimmune: Research Funding; FATE Therapeutics: Research Funding; ImmunoGen: Consultancy, Research Funding; Hanmi: Research Funding; Pfizer: Consultancy, Research Funding; Trillium: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Glycomimetics: Research Funding; Abbvie: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Data Monitoring Committee member; Dava Oncology (Arog): Consultancy; Celgene: Consultancy; Syndax: Consultancy; Shattuck Labs: Consultancy; Agios: Consultancy; Kite Pharmaceuticals: Consultancy; SOBI: Consultancy; STAR Therapeutics: Consultancy; Karyopharm: Research Funding; Newave: Research Funding.

© 2021 by The American Society of Hematology
2021
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