The research focuses on a protein called cell division cycle-associated protein 4, or CDCA4, a factor originally identified nearly a quarter century ago as a gene preferentially expressed in hematopoietic progenitors and mature blood cells. In recent years, CDCA4 has attracted growing attention in oncology. Pan-cancer analyses have flagged it as an oncogenic player in a range of human tumors, and separate studies have implicated it in bladder cancer progression through JAK/STAT signaling, in osteosarcoma development, and in radiotherapy resistance in colorectal cancer. What the new work adds is a detailed picture of how CDCA4 behaves in the specific context of chronic myeloid leukemia and its frontline therapy.

The team began with a broad computational sweep. A pan-cancer analysis revealed that high CDCA4 expression was significantly associated with shorter overall survival across multiple cancer types, establishing the protein as a plausible prognostic marker well before any leukemia-specific experiments were run. The investigators then turned to clinical material and laboratory models. Using quantitative real-time PCR, they measured CDCA4 levels in peripheral blood samples from chronic myeloid leukemia patients and in imatinib-resistant cell lines derived from the disease. In both settings, CDCA4 was upregulated, suggesting that the protein’s abundance rises precisely where drug resistance is the problem.

To test whether that correlation reflected causation, the researchers manipulated CDCA4 expression in leukemia cells and monitored the consequences. Cell proliferation assays based on the CCK-8 colorimetric method showed that forcing CDCA4 overexpression markedly enhanced resistance to imatinib and promoted the proliferation of chronic myeloid leukemia cells. In other words, simply raising the level of this one cell-cycle protein was enough to blunt the effect of the drug that has defined modern CML treatment. That result positions CDCA4 not as a passive bystander in resistant cells but as an active participant in the resistant phenotype.

The mechanistic heart of the study lies in what CDCA4 does once it is abundant. The team’s investigations indicated that CDCA4 is associated with hyperactivation of the AKT-mTOR signaling axis, a canonical growth and survival pathway that cancer cells frequently co-opt to evade stress and therapy. Alongside that hyperactivation, the researchers observed a concurrent suppression of basal autophagy, the cellular recycling process by which cells break down damaged components and survive metabolic hardship. The combination, the authors report, correlates with imatinib chemoresistance in chronic myeloid leukemia cells. This pairing is biologically coherent: AKT-mTOR signaling is a well-known negative regulator of autophagy, and prior work has shown that mTOR inhibition with compounds such as AZD2014 can alleviate BCR::ABL1-independent imatinib resistance by enhancing autophagy in resistant cells. The new findings slot CDCA4 into that same regulatory territory, upstream of the pathway shift that helps leukemic cells survive the drug.

Autophagy’s role in drug response has become one of the more contested questions in cancer biology, and the CML literature reflects that tension. Some studies have found that suppressing autophagy sensitizes leukemic cells to treatment, while others, including the mTOR-inhibition work referenced by this team, suggest that restoring autophagic flux helps resistant cells regain vulnerability. The new study comes down clearly on the side of autophagy as a tumor-suppressive process in this context: CDCA4-driven resistance travels with reduced basal autophagy, implying that leukemic cells which lose their recycling capacity, while simultaneously ramping up pro-survival AKT-mTOR signaling, are better equipped to withstand imatinib. Disentangling exactly how CDCA4 biases the balance between these two processes will be a task for future experiments, but the correlation the authors document is a concrete starting point.

Perhaps the most consequential discovery is what sits above CDCA4 in the regulatory hierarchy. Through molecular profiling, the team identified a circular RNA, hsa_circ_0029325, that governs CDCA4 expression levels. Circular RNAs are covalently closed loops of RNA generated by back-splicing, a form of non-canonical RNA processing that makes them unusually stable and resistant to degradation by exonucleases. Once dismissed as transcriptional noise, circular RNAs are now recognized as versatile regulators that can sponge microRNAs, interact with RNA-binding proteins, and in some cases even be translated into peptides. Their stability makes them attractive biomarkers, detectable in blood and other body fluids, and their regulatory reach makes them potential drug targets.

The connection between circ_0029325 and CDCA4 fits into a rapidly expanding catalog of circular RNA circuits implicated in drug resistance. Previous studies have linked circular RNAs to imatinib resistance through several routes: circ_SIRT1 has been shown to upregulate ATG12 and facilitate imatinib resistance by interacting with the splicing factor EIF4A3, circ_0080145 enhances resistance by regulating the miR-326/PPFIA1 axis, and hsa_circ_0058493 was identified as a biomarker of imatinib-resistant CML through microarray profiling. The supplementary data accompanying the new study add a further layer of mechanistic detail, showing that miR-503-5p, one of the microRNAs capable of targeting CDCA4, slows cell proliferation and increases imatinib sensitivity in the resistant K562-R cell line. Together these findings sketch a model in which circ_0029325 acts as a molecular sponge, sequestering CDCA4-targeting microRNAs such as miR-503-5p and thereby freeing CDCA4 to accumulate, hyperactivate AKT-mTOR signaling, dampen autophagy, and shield leukemic cells from imatinib.

The clinical implications are twofold. First, the circ_0029325-CDCA4-AKT axis offers a set of candidate biomarkers: measuring levels of the circular RNA, the protein, or downstream pathway activity could, in principle, help identify patients at risk of losing response before frank resistance emerges, allowing earlier switches to second- or third-generation tyrosine kinase inhibitors, which are already recommended in treatment algorithms for resistant or intolerant disease. Second, each node in the circuit is a potential therapeutic target. Antisense oligonucleotides or small interfering RNAs designed against circular RNAs are an active area of drug development, microRNA mimics have been explored as cancer therapeutics, and AKT and mTOR inhibitors are established pharmacological classes with oncology track records. A combination strategy that disrupts the circular RNA circuit while pharmacologically re-engaging autophagy could, the authors suggest, restore imatinib sensitivity in resistant cells.

Caveats remain, as they always do at this stage of translational research. The study’s clinical component rests on peripheral blood samples from patients at a single Chinese center, and the mechanistic work was performed largely in cell lines and animal models rather than in prospective patient cohorts. Whether circ_0029325 levels reliably predict resistance in a real-world monitoring setting, and whether intervening on the axis improves outcomes, will require validation studies with larger and more diverse populations. Still, the work is notable for connecting the dots across scales, from a pan-cancer survival analysis down to a specific circular RNA, its microRNA intermediaries, a cell-cycle protein, and the signaling and autophagy changes that ultimately determine whether a leukemia cell dies when imatinib arrives. For a disease in which the drug revolution is now more than two decades old, understanding why that revolution fails in some patients is one of the most important questions left in the field, and this study offers a concrete, testable answer to pursue.

Subject of Research: Circular RNA regulation of CDCA4 and the AKT-mTOR/autophagy axis in imatinib-resistant chronic myeloid leukemia

Article Title: Hsa_circ_0029325 drives imatinib resistance via the CDCA4/AKT axis in chronic myeloid leukemia

Article References: Lan, X., Sun, H., Mu, Y., Hou, X., Ti, C., Sun, W., Xie, S., Li, Y., & Sun, Y. (2026). Hsa_circ_0029325 drives imatinib resistance via the CDCA4/AKT axis in chronic myeloid leukemia. Molecular Biology Reports, 53(1), Article 1702. https://doi.org/10.1007/s11033-026-12904-6

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12904-6

Keywords: chronic myeloid leukemia, imatinib resistance, CDCA4, hsa_circ_0029325, circular RNA, AKT-mTOR signaling, autophagy, miR-503-5p, tyrosine kinase inhibitors, drug resistance, biomarkers, hematology

Chronic myeloid leukemia arises when a reciprocal translocation between chromosomes 9 and 22, the so-called Philadelphia chromosome, fuses the BCR gene on chromosome 22 with the ABL1 gene on chromosome 9. The resulting BCR::ABL1 protein is a constitutively active tyrosine kinase that drives uncontrolled proliferation of myeloid cells. Imatinib mesylate, the first-generation tyrosine kinase inhibitor approved in the early 2000s, binds the ATP-binding pocket of this aberrant kinase and switches off its signaling, converting a once uniformly fatal disease into a manageable chronic condition for the vast majority of patients. Treatment success is typically monitored by measuring levels of BCR::ABL1 transcript through reverse transcriptase PCR, with a deep molecular response, known as a major molecular response, serving as a key benchmark of effective therapy.

The Indian case began, as many do, with a diagnosis of Philadelphia-positive chronic myeloid leukemia and initiation of imatinib therapy. But the diagnostic workup immediately revealed something unusual. Fluorescence in situ hybridization, or FISH, a technique that uses fluorescently labeled DNA probes to detect specific genetic rearrangements in cells, produced an atypical signal pattern that did not fit the standard picture of a simple BCR::ABL1 fusion. Conventional karyotyping, in which chromosomes are stained and examined under the microscope, showed additional cytogenetic abnormalities beyond the expected Philadelphia chromosome, raising the possibility of complex rearrangements and clonal evolution, features that in chronic myeloid leukemia are usually harbingers of disease progression and poor response to therapy.

To resolve the puzzle, the team deployed a systematic combination of the three cornerstone tools of leukemia genetics. Conventional cytogenetics mapped the chromosomal architecture of the leukemic clone. FISH with probes targeting the ABL1 and ETV6 loci revealed the presence of two distinct fusion events rather than one. Finally, reverse transcriptase PCR confirmed at the transcript level that the patient’s cells harbored both BCR::ABL1 and ETV6::ABL1 fusions concurrently. The ETV6 gene, located on chromosome 12, encodes a transcription factor that is itself a frequent partner in pediatric leukemias when fused to ABL1, but the coexistence of ETV6::ABL1 alongside BCR::ABL1 within a single case of chronic myeloid leukemia is exceptionally rare, and the authors emphasize that such dual ABL1-rearranged presentations are seldom documented in the literature.

The clinical implications of this double hit are where the case becomes genuinely paradoxical. On one hand, the patient failed to achieve a major molecular response throughout the entire course of imatinib therapy, a pattern consistent with resistance. The presence of two ABL1-fused transcripts provides a plausible mechanistic explanation: the ETV6::ABL1 fusion, like BCR::ABL1, encodes an activated tyrosine kinase, but the two fusion transcripts may respond differently to the drug, and the additional cytogenetic abnormalities suggest a genetically complex clone whose full burden is not eliminated by imatinib’s inhibition of a single kinase species. In this sense, the case illustrates how cytogenetic analysis can serve as the pivotal tool for uncovering the underlying cause of apparent imatinib resistance, a point the authors single out as the key highlight of their study.

On the other hand, and contrary to what the genetic complexity would predict, the patient demonstrated long-term survival on continued imatinib therapy. Complex rearrangements and additional chromosomal abnormalities in chronic myeloid leukemia are classically associated with accelerated progression, blast crisis, and poor outcomes, yet this patient’s disease followed an indolent trajectory despite persistent molecular evidence of active leukemia. The authors describe this combination, resistance at the molecular level coexisting with a benign clinical course, as a paradox, and it is precisely this tension that makes the case scientifically valuable. It suggests that the biological aggressiveness conferred by dual ABL1 fusions and clonal evolution may not map neatly onto the conventional prognostic framework, and that molecular response benchmarks, while indispensable for most patients, may not tell the whole story in genetically unusual leukemias.

Why might a patient with two active kinase fusions remain clinically stable on a drug designed to inhibit one of them? The report does not claim to fully answer this question, but several considerations emerge from the biology of these fusions. The ETV6::ABL1 fusion, though oncogenic, has been associated in some reported cases with variable clinical behavior, and the relative abundance, kinase domain sequence, and downstream signaling intensity of each fusion transcript may differ substantially between patients. Moreover, imatinib does inhibit ABL1 kinase activity regardless of which partner gene drives its expression, meaning both fusion proteins are pharmacologically targeted to some degree. The persistent failure to reach major molecular response may therefore reflect the sheer genetic burden of a complex clone rather than true pharmacological escape, while the indolent course may reflect that the residual disease retained a chronic-phase biology rather than acquiring the additional hits needed for blast transformation.

Beyond its immediate clinical narrative, the case carries a broader message about diagnostics in the era of targeted therapy. Modern molecular monitoring for chronic myeloid leukemia is built almost entirely around quantitative PCR assays designed to detect canonical BCR::ABL1 transcripts. A patient whose leukemia contains a second, noncanonical fusion could, in principle, have that driver overlooked entirely if workup stops at routine molecular testing. It was the atypical FISH signal pattern, an anomaly that would have been easy to dismiss as technical noise, that triggered the deeper cytogenetic investigation and ultimately revealed the dual fusion architecture. The authors argue that systematic documentation of such rare cases is essential for the efficient management of patients and for evolving the field’s understanding of dual oncogenic drivers in myeloid neoplasms, a sentiment that underscores the enduring value of conventional cytogenetics even in an age dominated by next-generation sequencing.

The report also speaks to a persistent theme in current chronic myeloid leukemia research. As the authors note, the field’s primary focus has been the discovery of new tyrosine kinase inhibitors and the elucidation of mechanisms underlying imatinib resistance, from kinase domain mutations to compound abnormalities. Cases like this one broaden that agenda by showing that resistance-like molecular profiles can arise from structural genomic complexity, including concurrent fusions, rather than from point mutations alone. For clinicians, the practical takeaway is that unexplained failure to achieve molecular milestones on imatinib warrants a full cytogenetic re-evaluation, including karyotyping and extended FISH panels, before assuming classic resistance mechanisms or escalating therapy. For researchers, the case adds to the small but growing catalog of leukemias with multiple ABL1 rearrangements, a population whose natural history remains poorly characterized precisely because it is so rare.

Published as an open-access case report and conducted with institutional ethics approval and patient consent, the study is a reminder that individual patients with unusual biology continue to teach medicine its most unexpected lessons. A leukemia that should have been aggressive behaved gently; a therapy that should have failed clinically succeeded in keeping the patient alive for the long term even as molecular benchmarks remained unmet. Untangling that paradox required nothing more exotic than careful, layered application of karyotyping, FISH, and PCR, the classic triad of leukemia genetics, applied with the persistence to chase an atypical signal pattern to its root. As tyrosine kinase inhibitors continue to evolve and molecular monitoring grows ever more sophisticated, this rare dual-fusion case stands as both a caution against over-reliance on single-marker testing and an argument for keeping the older, slower tools of cytogenetics firmly in the diagnostic toolkit.

Subject of Research: Concurrent ETV6::ABL1 and BCR::ABL1 fusion genes in a rare case of chronic myeloid leukemia with imatinib resistance

Article Title: Concurrent ETV6::ABL1 and BCR::ABL1 in a rare case of chronic myeloid leukemia: a paradox of imatinib resistance and indolent clinical course

Article References: Mohanty, P., Shetty, D., Amare, P., Patkar, N., Tembhare, P., Subramanian, P. G., Punatar, S., Gokarn, A., Jindal, N., & Khattry, N. (2026). Concurrent ETV6::ABL1 and BCR::ABL1 in a rare case of chronic myeloid leukemia: a paradox of imatinib resistance and indolent clinical course. Annals of Hematology. https://doi.org/10.1007/s00277-026-07234-3

Image Credits: AI Generated

DOI: 10.1007/s00277-026-07234-3

Keywords: chronic myeloid leukemia, BCR::ABL1, ETV6::ABL1, imatinib resistance, tyrosine kinase inhibitor, cytogenetics, FISH, karyotyping, reverse transcriptase PCR, clonal evolution, myeloid neoplasms, ABL1 rearrangement