Re-evaluating absolute neutrophil count thresholds: Duffy-null-associated neutrophil count in cancer treatment.

The Duffy-null phenotype is associated with fewer circulating blood neutrophils. This phenomenon, termed Duffy-null-associated neutrophil count (DANC), is common among individuals of African and Middle Eastern ancestry. Despite growing evidence that DANC does not increase the risk of infectious complications, oncology treatment protocols often rely on standardised absolute neutrophil count (ANC) thresholds to guide chemotherapy dosing and clinical trial candidacy. This reliance risks inappropriate dose reductions or treatment delays in patients with DANC. We present a patient with DANC and high-volume metastatic hormone-sensitive prostate cancer in whom lower neutrophil counts, found to be due to DANC, delayed initiation of chemotherapy and led to the use of granulocyte-colony stimulating factor (G-CSF). This case highlights the dilemma that DANC may lead clinicians to delay chemotherapy and/or use G-CSF when neither may be needed. Future clinical studies are needed to develop DANC-specific thresholds for standard dose chemotherapy and G-CSF support.