Chronic myeloid leukemia (CML) is a hematologic malignancy characterized by the presence of the Philadelphia chromosome and the BCR-ABL1 fusion gene, an abnormal, cancer-causing gene created when pieces of chromosomes 9 and 22 break off and swap places.
The introduction of tyrosine kinase inhibitors (TKIs) has transformed CML from a fatal disease into a manageable chronic condition. However, achieving long-term disease control with minimal toxicity remains a central challenge, particularly for newly diagnosed patients requiring lifelong therapy. The recent ASC4FIRST pivotal trial and supporting clinical studies highlight the sustained superiority of asciminib (Scemblix®; Novartis Pharmaceuticals), a first-in-class STAMP inhibitor, over standard-of-care TKIs in terms of efficacy, safety, and tolerability at 144 weeks.
This review presents the long-term outcomes of asciminib in the frontline setting, including major molecular response (MMR), deeper molecular responses (MR4, MR4.5), and adverse event profiles, compared with imatinib (Gleevec®; Novartis Pharmaceuticals) and second-generation TKIs.
Imatinib, the first TKI approved for CML, revolutionized therapy but is associated with limitations in potency and resistance. Second-generation TKIs (nilotinib, dasatinib, bosutinib) improved molecular response rates and reduced progression to blast phase but did not significantly impact overall survival due to increased toxicity and non-CML-related mortality.[1][2] Asciminib, a STAMP inhibitor targeting the ABL myristoyl pocket, offers a novel mechanism of action distinct from ATP-competitive TKIs, with the potential to decouple potency from toxicity. [1][2][3]
ASC4FIRST Trial Design
ASC4FIRST (NCT04971226) is a multicenter, randomized, open-label Phase 3 study comparing oral asciminib (80 mg QD) to investigator-selected standard-of-care TKIs (imatinib, nilotinib, dasatinib, bosutinib) in 405 adult patients with newly diagnosed Philadelphia chromosome-positive chronic-phase CML (Ph+ CML-CP) (Hochhaus et al., 2024). Randomization was stratified by preselected TKI and EUTOS long-term survival (ELTS) risk groups.
The primary endpoint was MMR at week 48; secondary endpoints included deeper molecular responses and safety outcomes at subsequent time points.
Long-term Efficacy
At week 144, asciminib demonstrated a progressively greater advantage in molecular response rates compared to standard-of-care TKIs. Across the overall population, MMR was achieved in 77.1% of patients treated with asciminib versus 53.4% of patients receiving standard TKIs (difference, 23.7%; Hochhaus et al., 2024). In the imatinib stratum, MMR rates were 79.2% with asciminib versus 47.1% with imatinib alone (difference 32.1%). Among patients randomized to second-generation TKIs, asciminib achieved a 15.2% higher MMR rate (75.0% vs. 59.8%, P=0.01 nominal).
Deeper molecular responses were also superior in the asciminib group:
- MR4: 55.7% vs. 36.3% (overall), 58.4% vs. 33.3% (imatinib stratum), 53.0% vs. 39.2% (2G TKI stratum)
- MR4.5: 42.3% vs. 24.5% (overall), 43.6% vs. 19.6% (imatinib stratum), 41.0% vs. 29.4% (2G TKI stratum)
These results demonstrate that the efficacy gap between asciminib and comparator TKIs widens over time, with nearly 24% more patients achieving MMR compared to all standard TKIs and over 32% more compared to imatinib at week 144 [1]
Patient Retention and Treatment Durability
Long-term tolerability is critical for CML patients, who require continuous therapy. At week 144, more patients remained on treatment with asciminib than with standard TKIs (78.6% vs. 55.9%), imatinib (81.2% vs. 50.0%), and 2G TKIs (76.0% vs. 61.8%). These retention rates underscore asciminib’s suitability for chronic administration (Novartis, 2026).
Safety and Tolerability Profile
Asciminib’s safety profile at week 144 was consistent with previous long-term follow-up, with no new safety concerns observed (Hochhaus et al., 2024; Novartis, 2026). Compared to both imatinib and 2G TKIs, asciminib was associated with fewer grade ≥3 adverse events (AEs), fewer dose adjustments, and more than a 50% reduction in discontinuation due to AEs:
- Grade ≥3 AEs: 49% (asciminib) vs. 52% (imatinib) vs. 63% (2G TKIs)
- Discontinuation due to AEs: 6% (asciminib) vs. 13% (imatinib) vs. 14% (2G TKIs)
Dose adjustments/interruptions: 37% (asciminib) vs. 44% (imatinib) vs. 63% (2G TKIs)
The most frequent AEs (≥15%) were diarrhea, headache, fatigue, musculoskeletal pain, and rash. These findings reaffirm asciminib’s favorable tolerability profile, supporting its use for long-term therapy.
Interim Results and Genetic Insights
A phase II investigator-initiated trial at MD Anderson Cancer Center further supports asciminib’s efficacy and safety in newly diagnosed CML (Hachem et al., 2026). Among 59 patients treated with asciminib, the cumulative best overall response at 12 months included MCyR in 97%, CCyR in 92%, and MMR in 68%. The MMR rate among patients completing one year of therapy was 71%. Deeper responses (MR4, MR4.5) were achieved in 36% and 29% of patients, respectively.
Genetic analysis identified ASXL1 mutations in 7% of patients, with some cases of resistance associated with myristoyl pocket mutations (A337T, F497L, P465A, D381E). Adverse events included elevated lipase and fatigue, with three cases of pancreatitis and one fatal acute coronary syndrome. Overall, 14% discontinued therapy due to adverse events or resistance. Survival rates at 12 months were high: failure-free survival (92%), event-free survival (96%), and overall survival (98%) (NCT06236724)[1][2][3]
Mechanism of Action
Asciminib represents a new class of CML therapy by specifically targeting the ABL myristoyl pocket—a site distinct from the ATP-binding domain targeted by other TKIs. This specificity minimizes off-target toxicity and may reduce the risk of resistance associated with ATP-competitive inhibitors. [2][3] The STAMP mechanism enables asciminib to break the historical link between increased potency and increased toxicity, offering a more rapid and reliable pathway to long-term disease control.
Regulatory Status
Asciminib is approved for newly diagnosed adults with Ph+ CML-CP in more than 60 countries, including the US, EU, China, and Japan. It is also approved in 58 countries for previously treated adults with Ph+ CML-CP and for patients with the T315I mutation.
Clinical Implications and Unmet Needs
The long-term data from ASC4FIRST and phase II trials confirm asciminib’s role as an important frontline option for newly diagnosed CML. Its superior efficacy, safety, and tolerability address the critical issues of treatment adherence and disease control, particularly since CML is a lifelong condition for most patients. A favorable safety profile is essential to ensure that patients can remain on therapy without interruption due to adverse events.
Despite these advances, some challenges remain, including the emergence of resistance mutations within the myristoyl pocket and the need for ongoing research to optimize patient selection and management strategies. Further follow-up and real-world data will help clarify asciminib’s impact on long-term survival and quality of life.
Asciminib continues to demonstrate sustained superior efficacy and favorable safety at 144 weeks in patients with newly diagnosed CML, outperforming both imatinib and second-generation TKIs in achieving major molecular response and deeper molecular responses, with fewer serious adverse events and discontinuations. Its novel mechanism targeting the ABL myristoyl pocket offers a new paradigm in CML management, breaking the historical trade-off between potency and tolerability. The ASC4FIRST trial and supporting studies establish asciminib as a key option for frontline therapy, bringing hope for improved disease control and quality of life in CML.
Clinical trials
A Study of Oral Asciminib Versus Other TKIs in Adult Patients With Newly Diagnosed Ph+ CML-CP
ClinicalTrials.gov ID NCT04971226
Phase II Study Assessing Efficacy and Safety of Asciminib in Patients With Newly Diagnosed Chronic Myeloid Leukemia in Chronic Phase.
ClinicalTrials.gov ID NCT06236724
Highlights of prescribing information
Asciminib (Scemblix®; Novartis Pharmaceuticals)[Prescribing Information]
Imatinib (Gleevec®; Novartis Pharmaceuticals)[Prescribing Information]
Reference
[1] Hochhaus A, Wang J, Kim DW, et al.; ASC4FIRST Investigators. Asciminib in Newly Diagnosed Chronic Myeloid Leukemia. N Engl J Med. 2024 Sep 12;391(10):885-898. doi: 10.1056/NEJMoa2400858. PMID: 38820078.
[2] Hachem M, Haddad F, Jabbour E, Issa GC, Sasaki K, Nasr LF, Senapati J, Goulart H, Bataller A, Kadia TM, Stevens K, Castellano J, Montalban-Bravo G, Pemmaraju N, Dellasala S, Kantarjian HM. Phase II trial of asciminib for newly diagnosed chronic myeloid leukemia. J Clin Oncol. 2026;44(suppl 16):abstract 6589. doi:10.1200/JCO.2026.44.16_suppl.6589.
[3] Hughes TP, White DL, Yeung DT. Asciminib for Philadelphia chromosome-positive leukemias. Haematologica. 2025 Oct 1;110(10):2273-2280. doi: 10.3324/haematol.2024.286798. PMID: 40568725; PMCID: PMC12485309.
Featured image: Attendees during the ASCO Plenary Session, Chicago, IL. Photo courtesy 2023 © ASCO/Scott Morgan.
DOI
 has transformed CML from a fatal disease into a manageable chronic condition. However, achieving long-term disease control with minimal toxicity remains a central challenge, particularly for newly diagnosed patients requiring lifelong therapy. The recent ASC4FIRST pivotal trial and supporting clinical studies highlight the sustained superiority of asciminib (Scemblix®; Novartis Pharmaceuticals), a first-in-class STAMP inhibitor, over standard-of-care TKIs in terms of efficacy, safety, and tolerability at 144 weeks.){kind=link}