Polycythemia vera is a chronic myeloproliferative neoplasm in which the bone marrow produces too many red blood cells, driven in the vast majority of cases by the acquired JAK2 V617F mutation that keeps the JAK-STAT signaling pathway permanently switched on. Patients face elevated risks of thrombosis and, in high-risk disease, progression toward myelofibrosis or acute leukemia. Standard management has long relied on phlebotomy and cytoreductive agents such as hydroxyurea to keep blood counts down. Ruxolitinib, by contrast, is an oral targeted inhibitor of the Janus kinases JAK1 and JAK2, and it does double duty: it reduces the abnormal cell production driven by mutant JAK2 signaling while also damping down the inflammatory cytokine storm that these disorders generate, including pro-inflammatory mediators such as interleukin-6 and tumor necrosis factor. It is precisely this dual identity, cytoreductive and immunosuppressive at once, that made it the logical therapeutic experiment in this case.

The patient’s clinical course began conventionally enough. He was diagnosed with high-risk polycythemia vera and achieved hematologic complete remission on hydroxyurea, meaning his blood counts returned to and remained within normal ranges. More than five years later, however, he developed histiocytoid Sweet syndrome, an uncommon variant of a condition first described in 1964 by Robert Sweet as acute febrile neutrophilic dermatosis. Classic Sweet syndrome presents with fever, raised painful plaques and nodules, and skin biopsies showing dense infiltrates of mature neutrophils without evidence of infection. In the histiocytoid variant, the infiltrating cells are immature myeloid cells that resemble histiocytes under the microscope, expressing myeloperoxidase and often posing a genuine diagnostic challenge because they can mimic leukemia cutis, the skin infiltration of leukemic cells. Distinguishing the two matters enormously, because one is an inflammatory paraneoplastic phenomenon and the other signals overt malignant spread.

Sweet syndrome is classified into three broad categories: idiopathic or classic, drug-induced, and malignancy-associated. The malignancy-associated form most often accompanies hematologic cancers, including acute myeloid leukemia, myelodysplastic syndromes and the myeloproliferative neoplasms to which polycythemia vera belongs. The prevailing hypothesis is that the underlying clonal disorder somehow triggers a reactive, systemic inflammatory process in the skin, possibly through aberrant cytokine production by the abnormal hematopoietic cells themselves. This framing has a direct therapeutic consequence: in secondary or reactive Sweet syndrome, treating the underlying disease is considered a mainstay of therapy, not merely an adjunct. Yet the Swiss case pushes that principle into uncomfortable territory, because the underlying disease was, by every standard hematologic measure, already controlled.

Initial treatment of the skin eruption followed established practice. Corticosteroids produced a temporary complete resolution of the Sweet syndrome, which is the expected first-line response, since systemic steroids remain the most reliably effective therapy for this condition. The trouble came with tapering. At the first relapse, the eruption returned promptly whenever the prednisone dose was reduced below 10 milligrams daily, a pattern familiar to any clinician who has managed steroid-dependent inflammatory disease and a recipe for long-term steroid toxicity, including osteoporosis, diabetes, infection risk and adrenal suppression. The team then tried steroid-sparing alternatives. Both colchicine, a microtubule-disrupting agent widely used in neutrophilic dermatoses and autoinflammatory syndromes, and dapsone, an antibiotic with potent anti-neutrophilic properties, failed. The malignancy-associated histiocytoid Sweet syndrome proved refractory to both agents, leaving the patient dependent on corticosteroids with no conventional exit strategy.

At this point the treatment team made a decision grounded in pharmacological reasoning rather than precedent. Given ruxolitinib’s potent anti-inflammatory and immunosuppressive properties, and its established role in the treatment of polycythemia vera itself, they switched the patient’s cytoreductive therapy from hydroxyurea to ruxolitinib, aiming to treat both conditions with a single drug. The rationale rests on the biology of the JAK-STAT pathway. JAK1 and JAK2 transduce signals from a range of cytokine and growth factor receptors, and ruxolitinib’s inhibition of this axis suppresses not only the neoplastic clone in myeloproliferative neoplasms but also the downstream inflammatory signaling that is thought to drive paraneoplastic phenomena. In myelofibrosis, ruxolitinib is well known for reducing splenomegaly and, notably, for relieving constitutional symptoms such as night sweats and pruritus that are themselves cytokine-mediated, an effect that hinted at its broader immunomodulatory reach.

The gamble worked. Within six weeks of initiating ruxolitinib, the histiocytoid Sweet syndrome resolved completely, and the resolution proved durable: the patient maintained remission of the skin disease even after corticosteroids were discontinued entirely, while his polycythemia vera remained in hematologic remission throughout. The case therefore demonstrates two things simultaneously. First, it confirms that ruxolitinib can control steroid-refractory, steroid-sparing-agent-resistant Sweet syndrome in the setting of a myeloproliferative neoplasm. Second, and more conceptually important, it shows that clonal disease driving a paraneoplastic inflammatory syndrome can persist at a level undetectable by conventional hematologic monitoring. Hematologic complete remission, in other words, does not guarantee absence of the biological activity that fuels malignancy-associated Sweet syndrome, and the skin can serve as a sensitive readout of that residual activity.

The authors draw a practical conclusion from this that they state explicitly in their report: in patients with hematological malignancies and associated Sweet syndrome, modification of the underlying disease treatment may be considered even in the presence of hematologic complete remission, particularly when conventional Sweet syndrome therapies fail. This is a meaningful shift in emphasis. The traditional algorithm for malignancy-associated Sweet syndrome treats the skin disease and the cancer on parallel tracks, escalating skin-directed therapy with steroids, then steroid-sparing agents such as colchicine, dapsone, potassium iodide or cyclosporine, while cancer therapy proceeds independently. The Swiss case suggests that when the skin disease is refractory to that first tier, the smarter move may be to change the hematologic therapy itself, choosing an agent whose anti-inflammatory profile can reach the reactive process that conventional immunosuppressants cannot fully control.

There are, of course, the usual caveats that attach to any single-patient report. A case report establishes feasibility and biological plausibility, not efficacy; it cannot rule out spontaneous remission, and it cannot define the optimal dose, timing or patient selection for ruxolitinib in this setting. Ruxolitinib carries its own risk profile, including cytopenias and increased susceptibility to herpes zoster and other infections, which is why it is not a casual substitute for hydroxyurea in every patient. Nor is it yet clear whether the same strategy would work in Sweet syndrome associated with other hematologic malignancies, such as acute myeloid leukemia or myelodysplastic syndromes, where the cytokine milieu and clonal biology differ. What the case does establish is a testable hypothesis and a documented precedent, published with the patient’s written informed consent and conducted in accordance with the Declaration of Helsinki, that other clinicians can now build on.

Perhaps the most enduring message of the report is procedural rather than pharmacological: the authors emphasize that close collaboration between hematologists and dermatologists is essential in these cases. Histiocytoid Sweet syndrome sits precisely at the boundary between the two specialties, requiring dermatopathological expertise to distinguish it from leukemia cutis and hematological expertise to interpret what the skin eruption says about the state of the underlying clone. As targeted agents with immunomodulatory effects proliferate across oncology, the boundary cases are likely to multiply, and this Swiss patient’s six-week cure suggests that the most effective therapy for a paraneoplastic skin disease may sometimes be found not in the dermatology formulary but in the hematology one.

Subject of Research: Ruxolitinib treatment of histiocytoid Sweet syndrome associated with polycythemia vera

Article Title: Ruxolitinib-responsive histiocytoid sweet syndrome in a patient with polycythemia vera in hematologic remission – a case report

Article References: Rüfer, A., Senn, M., Kündig, T., & Zeerleder, S. (2026). Ruxolitinib-responsive histiocytoid sweet syndrome in a patient with polycythemia vera in hematologic remission – a case report. Annals of Hematology. https://doi.org/10.1007/s00277-026-07291-8

Image Credits: AI Generated

DOI: 10.1007/s00277-026-07291-8

Keywords: polycythemia vera, Sweet syndrome, histiocytoid Sweet syndrome, ruxolitinib, JAK inhibitors, hydroxyurea, corticosteroids, colchicine, dapsone, paraneoplastic dermatosis, myeloproliferative neoplasm, case report

The myeloproliferative neoplasms encompass essential thrombocythaemia, polycythaemia vera, prefibrotic primary myelofibrosis, and overt primary myelofibrosis, all disorders driven by mutated haematopoietic stem cells, most commonly carrying the JAK2V617F mutation. These conditions predispose patients to life-threatening blood clots and bleeding, and conventional cytoreductive therapy has primarily aimed at reducing this thrombotic risk. Hydroxyurea has long served as the default first-line option, yet it leaves 10 to 40 percent of patients intolerant or resistant, and lingering concerns about its long-term leukemogenic potential have fuelled the search for alternatives.

Interferon alpha occupies a fundamentally different therapeutic niche. Rather than simply poisoning dividing cells, this immunomodulating agent acts directly on haematopoietic stem and progenitor cells. Animal studies have shown that interferon alpha rouses quiescent malignant stem cells from dormancy, with a striking preference for cells carrying the JAK2V617F mutation, ultimately driving the malignant clone toward functional exhaustion. This disease-modifying potential, combined with the improved tolerability conferred by pegylation, prompted Danish investigators to design DALIAH as the earliest and largest randomised trial of long-term pegylated interferon in newly diagnosed patients across all myeloproliferative neoplasm subtypes.

Between February 2012 and July 2015, the trial enrolled 206 patients, of whom 203 formed the modified intention-to-treat population. Adults with newly diagnosed or treatment-naive disease were eligible regardless of risk score, a deliberate design choice that broadened the trial beyond the high-risk patients targeted by most prior studies. Older patients, aged over sixty, were randomised among hydroxyurea, pegylated interferon alpha-2a, or pegylated interferon alpha-2b, while younger patients avoided hydroxyurea owing to its theoretical leukemogenic risk and were randomised between the two interferon formulations. The cohort comprised 73 patients with essential thrombocythaemia, 89 with polycythaemia vera, 16 with prefibrotic myelofibrosis, and 25 with overt primary myelofibrosis. The median age was 62 years, and JAK2V617F was the dominant driver mutation, present in 74 percent of participants with a median baseline variant allele frequency of 34 percent.

The primary endpoint was the rate of molecular response, defined by European LeukemiaNet criteria as a substantial or complete reduction in the JAK2V617F variant allele frequency, measured serially by quantitative polymerase chain reaction at eight time points up to 60 months. By intention-to-treat analysis, which counted patients who discontinued treatment as non-responders, molecular response rates were statistically indistinguishable between the two drugs: 23 percent in the hydroxyurea arm versus 24 percent in the interferon arm at 60 months. This apparent parity, however, masks a profound divergence revealed when the analysis was restricted to patients who remained on their assigned therapy.

Among those who stayed the course, pegylated interferon proved decisively superior from 36 months onward. At that juncture, 56 percent of interferon-treated patients had achieved a molecular response, compared with just 23 percent of those on hydroxyurea, a gap that widened to 67 percent versus 35 percent by 60 months. Three interferon-treated patients reached complete molecular remission, with the JAK2V617F mutation rendered undetectable by an assay sensitive to 0.1 percent. Moreover, patients on hydroxyurea lost their responses far more frequently, with 62 percent losing molecular response versus only 13 percent of interferon patients, a difference that proved highly significant. The kinetics told a parallel story: the median relative reduction in variant allele frequency from baseline to 60 months was 75 percent with interferon compared with only 20 percent under hydroxyurea.

On secondary endpoints, the two drugs traded advantages. Complete clinicohaematological response at 12 months was similar between groups, and by intention-to-treat analysis hydroxyurea held a modest edge at 18 months, 58 percent versus 38 percent, though per-protocol analysis later favoured interferon at 36 and 60 months. Hydroxyurea normalised blood counts faster, with haematological response reached in a median of 1.6 months versus 3.8 months for interferon, a predictable consequence of its direct cytorepressive action. Conversely, more hydroxyurea patients lost their haematological responses over time, 86 percent compared with 44 percent on interferon. Bone marrow histopathology delivered an unexpected finding: by intention-to-treat analysis, histopathological remission at 60 months favoured hydroxyurea, 18 percent versus 5 percent, though paired analyses and per-protocol comparisons blurred this difference, and the investigators caution that fibrosis grading was inconclusive in significantly more hydroxyurea patients.

Safety data underscored the trial’s central challenge. At 60 months, 60 percent of all patients had discontinued study treatment, and discontinuation was significantly more frequent with interferon at 65 percent than with hydroxyurea at 37 percent. Toxicity drove the disparity: 45 percent of interferon patients stopped treatment for adverse events, most commonly flu-like illness, injection-site irritation, fatigue, and neuropsychiatric symptoms, while only 13 percent of hydroxyurea patients discontinued for that reason. Notably, discontinuation for toxicity clustered among younger and female patients and varied dramatically between study sites, from 30 to 69 percent, leading the authors to speculate that investigator enthusiasm may have shaped dosing decisions. Yet a subgroup of patients tolerated interferon long-term, and no treatment-related events of grade 3 or higher occurred beyond 24 months among those continuing therapy.

Thrombosis, the cardinal clinical concern in these diseases, was not prevented by interferon. Nineteen major thrombotic events occurred during treatment, with a rate of 5.5 events per 100 patient-years among older interferon patients versus 2.8 per 100 patient-years with hydroxyurea, a difference lacking statistical significance but clinically noteworthy. Importantly, 68 percent of thrombotic events occurred while blood counts remained normalised and before any substantial molecular reduction, reinforcing the multifactorial nature of clotting risk in myeloproliferative neoplasms. No patient progressed to myelofibrosis, acute myeloid leukaemia, or myelodysplastic syndrome, and five deaths were recorded across the cohort without an evident treatment-related pattern.

The DALIAH results arrive amid converging evidence that molecular response is not merely a laboratory curiosity. Data from the CONTINUATION-PV and MAJIC-PV trials link deepening JAK2V617F depletion with prolonged event-free survival, suggesting that eradicating the malignant clone may genuinely alter disease course. Within this framework, interferon’s slow but sustained molecular advantage, even as hydroxyurea’s responses eroded, positions low-dose pegylated interferon alpha-2a as a viable first-line option for carefully selected patients, particularly younger individuals in whom decades of cytoreductive therapy loom ahead. The trial’s authors call for biomarkers capable of predicting both response and tolerability at diagnosis, noting that mutated DNMT3A may confer interferon resistance. They also propose an intriguing strategy: an initial six to twelve months of combination therapy using hydroxyurea to rapidly normalise counts while interferon gradually strips away the malignant clone, followed by interferon monotherapy. With pegylated interferon alpha-2b withdrawn from the European market but alpha-2a still available and mono-pegylated ropeginterferon expanding the armamentarium, the era of disease-modifying first-line therapy for myeloproliferative neoplasms may finally be within reach.

Subject of Research: A five-year randomised phase 3 trial comparing pegylated interferon alpha with hydroxyurea as first-line cytoreductive therapy in myeloproliferative neoplasms.

Article Title: Interferon-α vs hydroxyurea in patients with myeloproliferative neoplasms (DALIAH): a multicentre, randomised, open-label, phase 3 trial in Denmark

Article References: Knudsen, T. A., Hansen, D. L., Ocias, L. F., Bjerrum, O. W., Brabrand, M., Christensen, S. F., Eickhardt-Dalbøge, C. S., Ellervik, C., El Fassi, D., Frederiksen, M., Kjær, L., Kristensen, T. K., Kruse, T. A., Larsen, M. K., Mourits-Andersen, T., Möller, S., Overgaard, U. M., Severinsen, M. T., Skov, V., … Hasselbalch, H. C. (2026). Interferon-α vs hydroxyurea in patients with myeloproliferative neoplasms (DALIAH): a multicentre, randomised, open-label, phase 3 trial in Denmark. eClinicalMedicine, 100, Article 104193. https://doi.org/10.1016/j.eclinm.2026.104193

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DOI: 10.1016/j.eclinm.2026.104193

Keywords: myeloproliferative neoplasms, pegylated interferon alpha, hydroxyurea, JAK2V617F, molecular response, DALIAH trial, polycythaemia vera, essential thrombocythaemia, primary myelofibrosis, phase 3 trial, cytoreductive therapy, haematology

Hydroxyurea has long been the cornerstone disease-modifying therapy for sickle cell anemia, the homozygous HbSS or HbSβ0-thalassemia genotypes that produce the most severe disease course. The drug works partly by reactivating fetal hemoglobin production, reducing the polymerization of sickle hemoglobin that drives red cell sickling, painful crises, and organ damage. Yet despite decades of clinical use, the precise relationship between dose and both clinical benefit and hematologic harm has remained uncertain, particularly across the diverse populations in which the disease is now treated.

To resolve this, the researchers conducted a systematic review and one-stage multilevel dose-response meta-analysis encompassing randomized trials, nonrandomized comparative studies, and longitudinal cohorts of children and adults with sickle cell disease. The quantitative synthesis focused principally on sickle cell anemia, with hydroxyurea dose expressed in mg/kg/day and achieved or maintenance doses preferred over starting doses. The primary benefit outcome was the rate of recurrent vaso-occlusive crises, while the primary safety outcomes were annual risks of severe or treatment-limiting neutropenia and thrombocytopenia, the two cytopenias that most often force dose reductions or discontinuation.

The modeling strategy was unusually rigorous. The team fitted Emax maximum-effect dose-response models as their primary analysis, testing linear and dose-independent alternatives in sensitivity analyses, and prespecified a decision rule requiring predicted annual neutropenia risk of no more than 5 percent and thrombocytopenia risk of no more than 3 percent, with at least an 80 percent simulation-derived probability that both criteria would be met simultaneously. Any eligible dose also had to retain near-optimal crisis control.

The results revealed a striking asymmetry between benefit and risk across the dose range. Empirical support for the primary analysis clustered between 20 and 28 mg/kg/day, and within that window recurrent vaso-occlusive crisis rates continued to fall, from a predicted 39.8 events per 100 person-years at 20 mg/kg/day to 32.5 at 28 mg/kg/day. Critically, the data showed no efficacy plateau: the Emax ED50 hit the upper limit of the prespecified search grid, and a simpler linear model actually fit marginally better, suggesting that whatever additional crisis reduction higher doses confer had not yet been exhausted within the observed range.

Safety told a different story. Predicted annual risk of severe or treatment-limiting neutropenia climbed steeply and early, from 1.98 percent at 20 mg/kg/day to 3.74 percent at just 21.5 mg/kg/day and 5.63 percent at 22.5 mg/kg/day. Thrombocytopenia, by contrast, remained uncommon and showed little dose dependence. Under the prespecified joint safety rule, the probability that both criteria were met was 87.1 percent at 20 mg/kg/day, 85.6 percent at 21 mg/kg/day, but only 77.8 percent at 21.5 mg/kg/day, failing the 80 percent threshold. The authors cautioned that because safety evidence was sparse and the joint classification depended partly on the relation between the two safety models, the low-20-mg/kg/day range should be read as an approximate safety transition rather than a precise toxicity threshold.

Within the empirically supported range, the lowest modeled recurrent crisis rate occurred at 28 mg/kg/day, and the unconstrained composite-benefit maximum at 25.5 mg/kg/day, but neither could clear the safety bar. Twenty-one mg/kg/day emerged as the highest dose satisfying the analytical rule, and the rounder conventional increment of 20 mg/kg/day was selected as the population reference dose, chosen from standard 2.5-mg/kg/day increments for practical prescribing.

The certainty of evidence behind these estimates was graded as very low for all three outcomes—recurrent crises, neutropenia, and thrombocytopenia—underscoring how much uncertainty remains. The review was prospectively registered with PROSPERO, and the authors emphasize that their decision framework, rather than any single trial, is what allows conflicting and sparse evidence to be converted into an actionable population-level recommendation.

Perhaps the most important clinical message is what the reference dose is not. The authors explicitly state that 20 mg/kg/day is neither a maximum tolerated dose nor a ceiling for treatment. Because crisis rates kept declining above 20 mg/kg/day, higher doses may well be appropriate for individual patients who need further clinical benefit, provided hematologic tolerance, adherence, and laboratory monitoring permit careful escalation. In resource-limited settings where laboratory surveillance is constrained, however, the population-level framework offers a defensible default that maximizes expected benefit while keeping predicted severe cytopenia risks within prespecified limits.

For the millions of people living with sickle cell anemia worldwide, most of them in sub-Saharan Africa, the findings translate decades of fragmented trial evidence into a single, transparent, quantitatively justified starting point for therapy—and a clear signal that the field still needs better safety data to push the benefit curve further.

Subject of Research: Dose-response relationship of hydroxyurea therapy in sickle cell anemia

Article Title: Hydroxyurea dosing in sickle cell anemia: a systematic review, dose-response meta-analysis, and population-level benefit-risk assessment

Article References: Hydroxyurea dosing in sickle cell anemia: a systematic review, dose-response meta-analysis, and population-level benefit-risk assessment. (n.d.). https://doi.org/10.1186/s12887-026-07679-5

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07679-5

Keywords: hydroxyurea, sickle cell anemia, dose-response meta-analysis, vaso-occlusive crisis, neutropenia, thrombocytopenia, benefit-risk assessment, systematic review, fetal hemoglobin, pediatric hematology, BMC Pediatrics, drug dosing