Which Factors May Contribute to a Successful Outcome in Hemophagocytic Lymphohistiocytosis: A Case Report.

Hemophagocytic lymphohistiocytosis (HLH) is a rare and life-threatening hyperinflammatory syndrome characterized by immune dysregulation and excessive cytokine activation. In adults, HLH is most commonly secondary to infections, malignancies, autoimmune diseases, or drug exposure. We report the case of a 50-year-old woman undergoing adjuvant treatment for human epidermal growth factor receptor 2 (HER2)-positive breast cancer who developed acute hypoxemic respiratory failure, neurological impairment, bicytopenia, marked hyperferritinemia, hypertriglyceridemia, and hepatomegaly. Extensive infectious, autoimmune, and neoplastic investigations were negative. The HScore, a validated diagnostic score for estimating the probability of secondary HLH in adults, was calculated at 211, corresponding to an estimated 93-96% probability of HLH. Following bone marrow examination demonstrating hemophagocytosis, the HScore increased to 246 (>99% probability). Chemotherapy was considered the probable trigger after exclusion of alternative causes. Treatment was initiated according to the HLH-94 protocol with dexamethasone, resulting in prompt clinical and laboratory improvement. The patient achieved full hematologic recovery and resumed oncologic therapy without HLH recurrence. This case highlights the importance of maintaining a high index of suspicion for HLH, systematic evaluation for underlying triggers, and prompt initiation of immunosuppressive therapy to improve patient outcomes.