A Non-interventional Study of Participants With BPDCN Treated With Chemotherapy

Inclusion Criteria: * Alive, deceased, or unreachable participants (as permitted by local regulation), aged ≥18 years at the start of first-line treatment for BPDCN, and treated with chemotherapy regimens (at a minimum) as first-line treatment for BPDCN from May 2016 * Diagnosed with BPDCN, based on clinical, laboratory, and imaging (where performed per institutional practice) assessments, with a demonstration of a specific immunophenotype (either by immunohistochemistry or flow cytometry), particularly CD4, CD56, and CD123 * Participants (or their legally authorized representatives) who have signed the informed consent and privacy form, where required as per local regulation Exclusion Criteria: * Participant has received an investigational agent as first-line therapy for BPDCN * Participant has received first-line therapy for BPDCN in an interventional clinical trial