A Case of Duffy-Null-Associated Neutropenia in a Patient With Chronic Myeloid Leukemia

Duffy-null-associated neutrophil count (DANC) refers to a below-normal absolute neutrophil count (ANC < 1.5 × 10³/L), present most commonly in African American individuals. Neutropenia is a result of a lack of Fya and Fyb antigens on red blood cells. These patients do not have an increased risk of infection and may have an ANC < 1.5 × 10³/L at baseline. This unique case presents Duffy-null-associated neutropenia in the setting of chronic myeloid leukemia (CML). A 64-year-old African American female presented to the emergency department on May 17, 2021, for fatigue and was found to have a white blood cell (WBC) count of 65.3 × 10⁹/L. Hematology and oncology referral led to a diagnosis of CML. Subsequently, she began treatment with imatinib (Gleevec) 400 mg daily. One month into treatment, she was neutropenic, with an ANC of 0.6 × 10³/L. For the next several years, this patient repeatedly had treatment holds and dose reductions in response to recurrent neutropenia. When BCR-ABL1 transcript level continued to increase, indicating poor treatment response, she was referred to Medical University of South Carolina (MUSC). After several treatment changes due to adverse effects, she began treatment with asciminib 80 mg daily. BCR-ABL1 transcript level with asciminib was consistently below 0.1%, indicating successful treatment response. Despite this milestone, she continued to have episodes of neutropenia, prompting a check for Duffy antigen presence. Testing confirmed the lack of Fya and Fyb antigens, indicating Duffy-null status. This case demonstrates the importance of identifying Duffy-null individuals. Despite achieving major molecular response, the patient had persistent neutropenia, leading to the investigation of Duffy-null status. It is hypothesized that underlying Duffy-null status may have caused neutropenia, rather than an adverse reaction to treatment. Early detection of Duffy-null status can prevent dose reductions in therapy and delayed remission. Particularly with African American patients, a better framework for addressing Duffy-null neutropenia may benefit long-term outcomes in the setting of cancer therapy.