April 2026 Research Update

This month, human treatment studies mostly focused on whether newer immune-targeting drugs can control HLH with less reliance on older, more intensive chemotherapy-based regimens. Across these studies, ruxolitinib (a JAK inhibitor that dampens immune over-activation) and rituximab (an antibody that removes certain B cells) were linked with meaningful responses in the groups studied, though the strength of evidence varied by setting. A separate small study explored a PD-1 inhibitor approach for EBV-associated HLH, with mixed individual outcomes and limited follow-up. [1] [2] [3] [4]

In newly diagnosed pediatric HLH, a response-guided regimen built around ruxolitinib was compared with the standard HLH-94 protocol. The ruxolitinib-based approach was reported to reach complete responses earlier and used less glucocorticoid and etoposide exposure during the first 8 weeks, while 12-month survival and reported safety looked similar between groups in this single-center comparison. This adds to the picture that some children may be able to reach control of inflammation with lower early exposure to the most intensive parts of standard therapy, but the comparison was not randomized. [1]

In children with HLH that was harder to control, a Japan-wide survey described ruxolitinib mostly as an add-on to conventional therapy, including use as maintenance in a few patients. Reported response rates were high in this collected experience, and the small maintenance group stayed in remission during the time described. This supports ruxolitinib as a commonly used real-world option in some pediatric centers, while still leaving open which patients benefit most and how it compares head-to-head with other strategies. [2]

For EBV-associated HLH, one retrospective analysis focused on cases where EBV infection involved B lymphocytes and reported that rituximab-containing regimens were followed by remission in most patients and EBV-DNA becoming negative in many of them. This fits a clear idea: when EBV is driving HLH through B cells, targeting those cells may help calm the disease by reducing the virus reservoir. The report did not compare rituximab regimens to a control group, so it cannot tell how much improvement was specifically due to rituximab versus the full treatment plans used. [3]

A very small real-world series in adults with EBV-associated HLH described use of the PD-1 inhibitor sintilimab, sometimes combined with ruxolitinib. Two people reached complete remission, one person could not be evaluated long-term, and one died from COVID-19-related multi-organ failure; severe drug-related side effects were not observed in this small group. This provides an early signal that PD-1 pathway treatment is being tried in EBV-HLH, but it remains early-stage evidence. [4]

For patients and caregivers, these studies add to a growing research direction: trying to control HLH inflammation with targeted immune medicines (like ruxolitinib or rituximab) that may reduce reliance on some of the most toxic parts of older regimens in certain settings. Some of this may matter now because these drugs are already being used in routine care in some centers, but the evidence here is mostly retrospective or single-center and does not settle which approach is best for a given person. What became clearer this month is that the "trigger" and underlying driver (such as EBV in B cells) can shape which targeted drug strategy is being tested. Many questions remain about long-term outcomes, the best timing, and how to compare options fairly in larger studies. [1] [2] [3] [4]

Several studies this month aimed to make HLH easier to recognize earlier and to understand what predicts worse outcomes in specific diseases. Together, they show that routine clinical clues and simple lab markers can sometimes separate higher-risk patients from lower-risk patients, even when classic findings like visible hemophagocytosis in the bone marrow are not present. These studies also reinforce that HLH is not one single illness, because the underlying trigger (infection, cancer, or immune treatment) can shape both how it looks and how severe it becomes. [5] [6] [7] [8] [9]

In adults with severe fever with thrombocytopenia syndrome (SFTS), researchers developed a model to estimate the chance of developing secondary HLH using data from the first 3 days after confirmation of SFTS. The model used six routine predictors, including fever features, spleen enlargement, triglycerides, fibrinogen, and ferritin, and it performed well in internal and external validation. For patients, the key point is that this kind of tool is trying to flag HLH risk early in a specific infection, but it still needs to prove it improves real-world outcomes when used in practice. [5]

In children hospitalized with scrub typhus, secondary HLH was reported as one of several serious complications, and having multiple severe manifestations was linked with a higher probability of a late response to doxycycline. This helps clarify that, in some infections, HLH appears as part of a broader pattern of organ involvement rather than a completely separate problem. The study described outcomes in one center and did not isolate HLH-specific treatment effects. [6]

In adults with acute myeloid leukemia (AML), a multicenter comparison reported that people who developed HLH had worse survival than AML patients who did not. HLH in AML could occur early after leukemia diagnosis, and visible hemophagocytosis in the bone marrow was present in only a minority of cases, meaning the diagnosis may rely on the overall clinical and lab picture rather than one single finding. This gives a clearer warning sign for patients: in AML, HLH may be a marker of a more severe course, even when standard marrow features are not obvious. [7]

In lymphoma-associated HLH, a multicenter adult cohort described which lymphoma types were seen and how features differed by HIV status, while noting that soluble IL-2 receptor levels were elevated in evaluable patients and mortality was high. This adds to the picture that, when HLH is tied to lymphoma, it often comes with strong immune activation signals and can be difficult to survive, although the report did not test a specific treatment approach. A separate observational study looked at presepsin, a blood marker related to immune cells, and found it rose along with inflammatory markers and with the percentage of hemophagocytes in bone marrow samples, suggesting it may reflect this process in the body. [8] [9]

For patients and caregivers, these studies mainly add understanding rather than changing what is done right away. They highlight that HLH can be missed or delayed if people wait for one "perfect" sign, because it can show up differently across infections and cancers, and marrow findings may be absent in some settings. The SFTS model and the presepsin work are examples of research trying to turn early clues into clearer risk signals, but they are not yet proven as tools that improve outcomes. What is clearer this month is that the underlying illness matters a lot: HLH in AML or lymphoma was linked with poor outcomes in these cohorts, while infection-related HLH appeared alongside broader severe disease. [5] [6] [7] [8] [9]

This month’s case reports and small case series emphasized how wide the HLH "trigger list" can be and how easily HLH can look unusual at first. Across these reports, HLH appeared after infections, cancers, immune disorders, and immune checkpoint inhibitor cancer therapy, and sometimes the initial clues were misleading or incomplete. A repeated message across cases is that tissue testing (biopsy) and targeted infectious or cancer workups were often needed to find the underlying driver. [10] [11] [12]

Several reports highlighted immune checkpoint inhibitors as a setting where HLH can occur and may be severe. One case described secondary HLH after atezolizumab in small cell lung cancer with an atypical presentation that lacked fever, making recognition harder, and the clinical course progressed despite intensive support. Two pharmacovigilance analyses of FAERS reports also found HLH reporting signals across checkpoint inhibitor classes, with higher signal strength reported for some agents and higher reporting odds in some combination regimens. [10] [13] [14]

A number of case reports showed HLH as a clue to an underlying cancer that required repeated or targeted biopsies to diagnose. One person met HLH criteria but had an initially negative bone marrow biopsy, and a PET/CT-guided repeat biopsy later identified diffuse large B-cell lymphoma followed by remission after immunochemotherapy. Other reports described HLH linked to NK/T-cell lymphoma diagnosed via liver biopsy guided by contrast-enhanced ultrasound, Kaposi sarcoma diagnosed by lymph node biopsy, and metastatic carcinoma of probable colorectal origin presenting first as HLH. [11] [12] [15] [16]

Infections were another common setting for secondary HLH in case reports and case series, including dengue, Rocky Mountain Spotted Fever, H1N1 influenza, Pneumocystis pneumonia, tuberculosis (where HLH was suspected but could not be fully confirmed), and EBV-related illness. The outcomes varied widely, with some patients stabilizing or reaching remission and others progressing despite intensive support. The EBV-related pediatric case series also described severe ENT complications of infectious mononucleosis, including one case where HLH occurred during the course. [17] [18] [19] [20] [21] [22] [23]

Several reports focused on HLH in the context of immune or genetic conditions, including pregnancy with adult-onset Still's disease, Kabuki syndrome, DiGeorge syndrome, reticular dysgenesis due to an AK2 variant, and prenatal diagnosis of familial HLH due to a PRF1 variant. These cases underline that in some families or immune disorders, HLH can be part of a broader immune system problem and may present very early in life, even before birth. A separate case described a child with predominant brain involvement where imaging and brain biopsy supported HLH, illustrating how HLH can sometimes center on the nervous system. [24] [25] [26] [27] [28] [29]

A few additional individual reports described less common HLH-linked situations, including aggressive NK cell leukemia presenting with HLH, suspected AML-associated HLH after a dengue-like illness, HLH arising during complex inflammatory and catheter-related sepsis in DGKE-related thrombotic microangiopathy, and splenic necrosis detected by contrast-enhanced ultrasound in a patient with myelodysplastic syndrome and hemophagocytic syndrome. Taken together, these add examples of how HLH can complicate already complex illnesses and why the underlying diagnosis can matter as much as the HLH label itself. [30] [31] [32] [33]

For patients and caregivers, these case reports mainly broaden awareness of how HLH can present, rather than proving that a specific approach works for most people. The practical meaning is that HLH is often a reaction to something else (like an infection, cancer, or an immune-related medication), and these reports show that finding that "something else" sometimes required repeat biopsies, specialized imaging guidance, or genetic testing. The checkpoint inhibitor reports add to existing concerns about HLH as a rare but serious immune-related side effect, and the FAERS analyses suggest it is being reported across multiple drugs and combinations. What remains uncertain is how often these unusual presentations occur and which warning signs best predict HLH early, because single cases cannot provide reliable rates or rules. [10] [13] [14] [11] [27] [28]