Sumitomo Pharma America has won FDA Breakthrough Therapy Designation for enzomenib, an investigational oral drug for a genetically defined form of acute leukemia — the company's fourth FDA designation for the drug since 2022, and a step that speeds up regulatory review for a treatment that still trails two already-approved rivals to market.
Enzomenib's record in four figures
Figures from Sumitomo Pharma America's own conference presentations and designation announcements, 2024-2026.
From six companies to one Marlborough pipeline
Enzomenib's development sits inside Sumitomo Pharma America, the Marlborough, Massachusetts drug maker formed on 1 July 2023 when Sunovion Pharmaceuticals, Sumitomo Pharma Oncology and four other Sumitomo-owned US biotechs consolidated into one company. The drug itself traces further back, to Tolero Pharmaceuticals and Boston Biomedical, two oncology biotechs that merged in 2020 to form the unit that first advanced DSP-5336 toward the clinic.
Enzomenib's four-designation path since 2022
- 1 July 2020
Sumitomo Dainippon Pharma Oncology formed
Tolero Pharmaceuticals and Boston Biomedical merge to form the oncology unit that would develop DSP-5336, later renamed Sumitomo Pharma Oncology.
- June 2022
Orphan Drug Designation (AML)
FDA grants enzomenib orphan drug status for acute myeloid leukemia.
- 1 July 2023
Sumitomo Pharma America formed
Sunovion Pharmaceuticals, Sumitomo Pharma Oncology and four other US affiliates consolidate into Sumitomo Pharma America, Inc.
- 15 July 2024
Fast Track Designation
FDA grants enzomenib Fast Track status for relapsed or refractory AML with a KMT2A rearrangement or NPM1 mutation.
- 4 October 2025
ASH 2025 data cutoff
Company-reported data on 116 patients treated across dose-escalation and dose-expansion cohorts, presented at the American Society of Hematology annual meeting.
- 30 July 2026
Orphan Drug Designation (ALL)
FDA grants enzomenib a second orphan drug designation, this one for acute lymphoblastic leukemia.
- 26 October 2026
Breakthrough Therapy Designation
FDA grants enzomenib Breakthrough Therapy status for relapsed/refractory KMT2A-rearranged acute leukemia.
- Expected late 2026
Horizen-1 interim analysis
Sumitomo has said the registrational Phase 2 portion of Horizen-1 reached the patient count needed for an interim analysis, with results expected by the end of 2026.
A fourth designation, not yet an approval
FDA's Breakthrough Therapy Designation, announced 26 October 2026, is enzomenib's fourth FDA designation since 2022 and its most consequential yet: it adds mechanisms for more frequent FDA interaction, organizational commitment and other tools meant to speed development toward approval. It is not an approval, and it does not change the Phase 1/2 Horizen-1 trial's own path to registrational data.
“Patients with R/R KMT2A-rearranged acute leukemia continue to face poor outcomes. [FDA’s] decision to grant breakthrough therapy designation underscores enzomenib’s potential and enables expedited FDA review that may potentially provide the opportunity to bring this investigational treatment to patients more quickly.” Tsutomu Nakagawa, PhD, President and Chief Executive Officer, Sumitomo Pharma America — 26 October 2026 announcement
What makes a menin inhibitor work
Enzomenib is an oral, small-molecule drug designed to block the interaction between menin and KMT2A (also known as MLL), a protein pairing that drives leukemia-cell growth in patients whose cancer carries a KMT2A gene rearrangement or, in some rival drugs' indications, an NPM1 mutation. It is evaluated as monotherapy in the registrational portion of the Phase 1/2 Horizen-1 trial, and in combination with standard chemotherapy regimens in earlier cohorts of the same master protocol.
Three things that separate enzomenib's path from its rivals'
A broader KMT2A population
Where Syndax's already-approved Revuforj is indicated for relapsed/refractory acute leukemia with a KMT2A translocation, Sumitomo frames enzomenib's Breakthrough Therapy Designation around KMT2A-rearranged acute leukemia broadly, spanning both AML and ALL.
Four designations in four years
Enzomenib has collected an Orphan Drug Designation for AML (2022), Fast Track (2024), a second Orphan Drug Designation for ALL (2026) and now Breakthrough Therapy (2026) — a ladder that accelerates FDA review without itself constituting approval.
Behind two approved rivals
Revumenib and ziftomenib already carry FDA approval in overlapping indications; enzomenib's designation buys faster FDA engagement for a drug that still has to clear the approval bar both of them have already cleared.
Third into a class two rivals already lead
Enzomenib is not the first menin inhibitor to reach this point, and it will not be the first approved. Syndax Pharmaceuticals' revumenib, sold as Revuforj, won FDA approval in November 2024 for the identical core population — relapsed or refractory acute leukemia with a KMT2A rearrangement — and Kura Oncology and Kyowa Kirin's ziftomenib, sold as Komzifti, followed roughly a year later for NPM1-mutated relapsed/refractory AML, a population that overlaps with enzomenib's own target group. Breakthrough Therapy Designation accelerates Sumitomo's path toward a decision; it does not change that two rivals are already on pharmacy shelves.
What an increasingly crowded leukemia class is worth
$3.8B → $6.1B
Global acute myeloid leukemia (AML) treatment market, 2023 to 2028, as forecast by BCC Research.
Sources: BCC Research, Acute Myeloid Leukemia (AML) Market report · ResearchAndMarkets, via BusinessWire: menin inhibitor market opportunity, 2024-2028
Regulatory News outlook
We expect enzomenib to compete for a slice of a menin-inhibitor segment ResearchAndMarkets sizes at more than $400 million through 2028 across 15-plus clinical-stage drugs, rather than expand the broader AML market on its own; two rivals already hold FDA approval in overlapping indications.
How we got here: BCC Research's published figures put the broader AML treatment market at $3.8 billion in 2023, rising to $6.1 billion by 2028, roughly a 10% compound annual growth rate; we treat the menin-inhibitor segment ResearchAndMarkets separately sizes at over $400 million through 2028 as the more relevant near-term opportunity for a drug still in designation-stage development, not yet approved.
Enzomenib against the menin inhibitors already ahead of it
| Product | Maker | US status | Indication |
|---|---|---|---|
| Enzomenib (DSP-5336) | Sumitomo Pharma America | Investigational; FDA Breakthrough Therapy Designation, Oct 2026 | R/R KMT2A-rearranged acute leukemia |
| Revuforj (revumenib) | Syndax Pharmaceuticals | FDA approved, Nov 2024 | R/R acute leukemia with a KMT2A translocation, adult and pediatric |
| Komzifti (ziftomenib) | Kura Oncology / Kyowa Kirin | FDA approved, Nov 2025 | R/R NPM1-mutated AML |
| BMF-219 | Biomea Fusion | Phase 1, investigational | AML, ALL and other hematologic cancers |
From each company's own FDA designation and approval announcements; not a clinical comparison.
What interim data has to show by Q4
Breakthrough Therapy Designation accelerates FDA's engagement with Sumitomo; it does not change what the drug has to prove. Horizen-1's interim analysis, expected before the end of 2026, is the next concrete checkpoint — and the first chance to see whether enzomenib's early response-rate data (57% ORR in 21 evaluable patients at EHA 2024; 116 patients treated with no new dose-limiting toxicities by the ASH 2025 cutoff) holds up at registrational scale, in a field where two rivals already have FDA approval in hand.
- Designation: FDA Breakthrough Therapy Designation for enzomenib (DSP-5336), announced 26 October 2026, for relapsed/refractory KMT2A-rearranged acute leukemia.
- Not an approval: enzomenib remains investigational; the designation accelerates FDA review and interaction, it does not authorize marketing.
- Already-approved rivals: Syndax's revumenib (Revuforj, Nov 2024) and Kura Oncology/Kyowa Kirin's ziftomenib (Komzifti, Nov 2025) both hold FDA approval in overlapping indications.
- Next checkpoint: Horizen-1's registrational Phase 2 interim analysis, which Sumitomo has said is expected by the end of 2026.
Sources & further reading
- Sumitomo Pharma America, FDA Breakthrough Therapy Designation announcement for enzomenib (via BusinessWire), 26 October 2026. financialcontent.com
- OnClive, "FDA Grants Breakthrough Therapy Designation to Enzomenib in R/R KMT2A-Rearranged Acute Leukemia." onclive.com
- TargetedOnc, "Enzomenib Earns FDA Breakthrough Status in KMT2A-Rearranged Leukemia." targetedonc.com
- PharmaShots, "Sumitomo Pharma America's Enzomenib (DSP-5336) Receives the US FDA's Breakthrough Therapy Designation for R/R KMT2A-Rearranged Acute Leukemia." pharmashots.com
- ClinicalTrials.gov, Horizen-1 (A Phase 1/2 Study of Enzomenib (DSP-5336) in Patients With Acute Leukemia), NCT04988555. clinicaltrials.gov
- Syndax Pharmaceuticals, FDA approval announcement for Revuforj (revumenib), November 2024, via BioSpace. biospace.com
- PharmaFocus Asia, "Kura Oncology and Kyowa Kirin Receive Approval for Komzifti," November 2025. pharmafocusasia.com
- BCC Research, Acute Myeloid Leukemia (AML) Market report. bccresearch.com
Regulatory News reports on public regulatory documents. It is not legal advice, and the primary sources above govern. If we have made an error, we will say so in public: see corrections.
Frequently asked questions
What did FDA grant Sumitomo Pharma America?
Breakthrough Therapy Designation for enzomenib (DSP-5336), an investigational oral menin-KMT2A inhibitor, for relapsed/refractory KMT2A-rearranged acute leukemia. The designation, announced 26 October 2026, speeds up FDA's engagement with the drug's development; it is not an approval, and enzomenib is not yet on the market.
Is enzomenib the first drug of its kind?
No. Syndax Pharmaceuticals' revumenib (Revuforj) won FDA approval in November 2024 for the identical core population, and Kura Oncology/Kyowa Kirin's ziftomenib (Komzifti) followed in November 2025 for an overlapping NPM1-mutated AML population. Enzomenib would be the third oral menin inhibitor to reach the US market, not the first.
What is Horizen-1?
The Phase 1/2 trial (NCT04988555) evaluating enzomenib, both as monotherapy in its registrational Phase 2 portion and in combination with standard chemotherapy regimens in earlier cohorts of the same protocol. Sumitomo has said the registrational portion reached the patient count needed for an interim analysis, with results expected by the end of 2026.
Is Sumitomo Pharma America a public company?
Not on its own. It is the wholly owned US subsidiary of Sumitomo Pharma Co., Ltd. (Tokyo Stock Exchange: 4506), formed in July 2023 from the consolidation of Sunovion Pharmaceuticals and several other Sumitomo-owned US biotechs.
