The purpose of this study is to build the knowledge base on clinical characteristics, clinical management, and treatment outcomes of HES.

Retrospective database analysis using TriNetX database to describe HES patient characteristics, journey, and disease burden.

Inclusion Criteria:

• Diagnosis record of HES (ICD-10-CM D72.11) anytime during 01 October 2020 to 30 June 2023
• At least 12 months of patient insurance record prior to first HES record.

Exclusion Criteria:

• Any mutation in PDGFRA, PDGFRB or FGFR1 genes (to exclude clonal HES).
• History of BCR-ABL tyrosine kinase inhibitor use: imatinib, dasatinib, nolitinib, bosutinib, ponatinib, asciminib (to exclude clonal HES)
• History of myeloid leukemia, myeloproliferative disorder, myelodysplastic disorder, myelomonocytic leukemia, acute erythroid leukemia, acute megakaryoblastic leukaemia, acute panmyelosis with myelofibrosis, and other specified leukaemias (to exclude reactive HES)
• History of helminthiasis or use of anthelmintic medication (to exclude reactive HES)
• History of autoimmune disease (to exclude reactive HES)
• History of use of specific drugs: antiepileptics, sulfonamides, allopurinol, and immune checkpoint inhibitors (to exclude reactive HES)

The study population is patients with HES during the period 01 October 2020 to 30 June 2023 available in TrinetX database (US).