Dengue fever is a highly prevalent arboviral infection in tropical and subtropical regions, including Brazil, where recurrent outbreaks impose a significant public health burden. While it usually presents as a self-limited febrile illness, immunocompromised patients, particularly those with oncohematological diseases, are at higher risk of severe complications. Immune dysfunction in these patients is often aggravated by chemotherapy, immunotherapy, or corticosteroid use. Despite dengue’s high prevalence in Brazil, data on its impact in this population are scarce.

We aimed to describe the clinical profile, hematological parameters, treatment, and outcomes of dengue infection in oncohematological patients treated at Sírio-Libanês Hospital between 2024 and 2025.

We retrospectively analyzed 16 oncohematological patients with confirmed dengue during the study period in Sírio Libanês Hospital.

Most cases (11/16) occurred in April–May 2024, in line with national seasonality. The majority were male (81%), median age 70.5 years. Diagnoses included lymphoproliferative diseases (50%), multiple myeloma/amyloidosis (31%), myelodysplastic syndrome (12%), and myeloproliferative neoplasms (6%). Median baseline platelet count before infection was 160,000/mm³; nadirs during infection fell to a median of 58,000/mm³ (range 5,000– 394,000/mm³). Median hematocrit during infection was 35.5% (26–45%). Based on severity stratification, 12 patients were group B and 4 group D; none were group A. Eleven required hospitalization, one in intensive care. Four received platelet transfusions, one corticosteroids. Three patients died: two elderly (88 and 93 years) from septic shock and one younger patient with relapsed refractory myeloma from central nervous system hemorrhage. All fatalities had platelet nadirs of 5,000/mm³, required platelet transfusions, and were under active chemoimmunotherapy at the time of infection.

Dengue in oncohematological patients poses unique challenges. Hematocrit, a classic severity marker, proved unreliable due to baseline anemia from malignancy and treatment. The 18.7% mortality rate was concentrated in patients receiving active chemoimmunotherapy, underscoring the profound vulnerability of this subgroup. Deaths in elderly patients reflected the additive risks of advanced age, immunosuppression, and severe infection, while the hemorrhagic death in the younger patient highlighted the extreme bleeding risk from severe thrombocytopenia. These findings reinforce the need for vigilant monitoring, rapid detection of complications, and individualized management strategies in dengue cases among oncohematological patients, especially those undergoing chemoimmunotherapy. Further studies are needed to guide preventive and therapeutic approaches in this high-risk population.