Purpose: To improve clinical decision-making in patients with breast cancer receiving CDK 4/6 inhibitors, we examined Duffy status and relative medication titration rates at Boston Medical Cancer Center.

Methods: We performed a retrospective chart review of patients with breast cancer receiving CDK 4/6 inhibitors at Boston Medical Center between January 1, 2021 and June 1, 2024.

Results: Of the 71 patients included, race was White in 21% and Black in 54%, where 90% of patients with Duffy-null associated neutrophil count (DANC) were Black. When stratifying by Duffy status, Duffy non-null (38/71) and null patients (21/71) had median pre-treatment nadir absolute neutrophil count (ANC) 2.6 (IQR 1.8) and 1.7 (IQR 1.0) and post-treatment nadir ANC 1.6 (IQR 1.2) and 1.0 (IQR 0.6). Overall, no patients meeting criteria for grades 3-4 neutropenia were hospitalized for neutropenic fever. Older patients had higher odds of dose reduction or treatment delay (adjusted odds ratio [aOR] 3.04, 95% confidence interval [CI] 1.06-9.07). However, patients with DANC had no significant differences in rates of dose reduction or treatment delay (aOR 1.31, 95% confidence interval (CI) 0.37-4.73).

Conclusion: Despite having lower ANC than their non-null counterparts, Duffy null patients on CDK 4/6 inhibitors received standard starting doses without significant differences in dose reduction or treatment delay.

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2025
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