Hemophagocytic syndrome (HS) is a rare condition that can be responsible for severe organ failure. Therapeutic guidelines are mainly based on observational studies and expert opinions: no therapeutic advance has been developed for years, explaining why mortality in HS remains high (Intensive Care Unit mortality ranging from 40 to 70%). If etoposide remains the gold standard in critically ill HS patients, nearly 20% of patients are refractory to this therapy: treatment escalation is common, most often requiring the administration of intensive treatments generating high toxicity. Ruxolitinib is the first approved JAK inhibitor. It has been associated with improvement of HS manifestations and survival in a pre-clinical murine model. Data in humans are scarce but promising.

The aim is to demonstrate that ruxolitinib, in association with standard of care, may reverse organ failure (as represented by Sequential Organ Failure Assessment (SOFA) score) better than standard of care alone in critically ill patients with acquired HS.

Inclusion Criteria:

• adult patients older than 18 years

• acquired hemophagocytic syndrome, regardless of etiology, defined by the presence of 5 or 6 HLH-2004 criteria or HScore ≥ 200

• admission in the ICU

• need for symptomatic treatment of HS in relation with organ failure, as defined by SOFA score ≥ 4

• Informed consent signed:

  • by the patient,
  • Or informed consent signed by a family members/trustworthy person if his condition does not allow him to express his consent in written

• Or in an emergency situation and in the absence of family members/trustworthy person, the patient can be enrolled. The consent to participate to the research will be requested as soon as the condition of the patient will allow).

• The inclusion of women of childbearing potential requires the use of a highly effective contraceptive measure. Contraception should be maintained during treatment and one day after

Exclusion Criteria:

• Moribund, defined by a life expectancy < 48 hours;
• Pregnant or lactating patients (women of childbearing potential must have a negative urine or blood Human Chorionic Gonadotropin pregnancy test prior to trial entry);
• No affiliation to health insurance;
• Known hypersensitivity to ruxolitinib;
• Lactose intolerance;
• Hypersensitivity to cellulose, microcrystalline; magnesium stearate; silica, colloidal anhydrous; sodium starch glycolate (Type A); povidone K30; hydroxypropylcellulose 300 to 600 cps,
• Pre-existing decisions of withholding/withdrawing care,
• History of progressive multifocal leukoencephalopathy
• Uncontrolled cutaneous cancer
• Persons under psychiatric care that would impede understanding of informed consent and optimal treatment and follow-up
• Adults subject to a legal protection measure (guardianship, curatorship and safeguard of justice)
• Patients deprived of their liberty by a judicial or administrative decision
• Participation in another interventional research