Abstract PS4-09-06: Retrospective evaluation of neutropenia and Duffy-Null Associated Neutrophil Counts (DANC) among breast cancer patients receiving chemotherapy

Abstract Background: Duffy-Null Associated Neutrophil Count (DANC) is a non-pathologic state characterized by a low absolute neutrophil count (ANC) without increased risk of infections. Approximately 60% of people identifying as Black are estimated to have the Duffy-null phenotype, and Duffy-null phenotype is also seen in people of Middle Eastern descent and Hispanic ethnicity. Cancer patients (pts) with DANC have often been excluded from clinical trials due to low ANC and may receive inappropriate dose delays or reductions of standard anticancer therapy. Testing for Duffy-null phenotype is readily available, but no standard of care exists for management of chemotherapy dosing in breast cancer (BC) pts with DANC. There is little data assessing the impact of low baseline ANC and Duffy-null phenotype on chemotherapy dose delays and dose reductions in triple-negative breast cancer (TNBC) pts. We conducted a retrospective study evaluating baseline ANC, chemotherapy dose delays and reductions, and use of Duffy antigen testing, in pts with TNBC treated at our institution, an urban academic medical center. Methods: Pts with Stage I to III TNBC treated from 2016 to 2021 were identified from the Montefiore Einstein Comprehensive Cancer Center (MECCC) tumor registry. Baseline ANC levels were correlated with dose reduction, delay or discontinuation of chemotherapy using logistic regression models, while adjusting for stage, chemotherapy regimen, baseline white blood count cell and absolute neutrophil count, as well as race and ethnicity. Results: 159 pts [77 (48%) Black, 69 (43%) Hispanic] met inclusion criteria. Median age was 59 yrs. 50 pts (31.4%) received chemotherapy in the neoadjuvant setting, 80 pts (50.3%) in the adjuvant setting, and 29 pts (18.2%) in both. 94 pts (59.1%) received anthracycline and taxane based chemotherapy; 41 pts (25.8%) received taxane without anthracycline; 24 pts (15.1%) received neither agent. Median baseline ANC was lower in Black pts than in Hispanic or Non-Hispanic white (NHW) pts (p=0.034), but no racial or ethnic differences in dose delays, dose reductions, early chemotherapy discontinuation, or neutropenic fever were seen. Low baseline ANC (defined as baseline ANC below the median level for each race/ethnicity group) was associated with higher likelihood of chemotherapy dose delay for neutropenia compared to high baseline ANC (38% vs 16%, p=0.002), and with trend to higher likelihood of dose reduction for neutropenia (18% vs 7.4%, p = 0.056). Within the low ANC group, those with dose delays had a lower baseline. ANC value as compared with those that did not have dose delays (1.7 vs 2.7, p<.001), but no correlations between baseline ANC and neutropenic fever was seen (ANC 2.8 vs 2.6, p=0.9). Three pts in our cohort had been told of low ANC prior to BC diagnosis: one underwent early discontinuation of chemotherapy due to neutropenia, and two experienced dose delays and dose reductions. No pt underwent formal testing for Duffy-null phenotype. Conclusion: In our diverse cohort of TNBC BC pts, Black pts had lower baseline ANC than Hispanic or NHW pts, but did not have more chemotherapy dose delays or reductions for neutropenia, and did not have higher risk of neutropenic fever. Lower baseline ANC, regardless of race or ethnicity, was associated with greater likelihood of chemotherapy dose delays and reductions for neutropenia, but not with higher risk of neutropenic fever. Testing for Duffy-null phenotype in pts with low ANC was not utilized. Duffy antigen testing of TNBC pts with low ANC may reduce unwarranted chemotherapy dose reductions or delays. Prospective evaluation of the utility of Duffy antigen testing in BC pts is warranted, and testing should not be limited to Black patients. Guidelines for management of chemotherapy dosing in BC pts with DANC should be developed. Citation Format: B. Chadha, Y. Xu, R. Hadidchi, T. Duong, X. Xue, D. Levitz, D. Makower. Retrospective evaluation of neutropenia and Duffy-Null Associated Neutrophil Counts (DANC) among breast cancer patients receiving chemotherapy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-09-06.