Evaluation of sacituzumab-induced severe or febrile neutropenia and G-CSF utilization and cost for advanced HER2- breast cancer.

e23259 Background: Sacituzumab govitecan-hziy (Saci) is an antibody-drug conjugate approved for patients (pts) with unresectable or metastatic triple-negative breast cancer (TNBC) or HR+/HER2- breast cancer. Neutropenia is a common toxicity, with rates of febrile neutropenia (FN) and severe neutropenia (SN; grade 3 or 4) reported in initial landmark trials at 4-6% and 51%, respectively. These adverse events can lead to treatment delays, discontinuation, hospitalization, or life-threatening complications. Based on Saci’s FN risk category, granulocyte colony-stimulating factor (G-CSF) is typically considered secondary prophylaxis unless specific risk factors warrant primary use. This study evaluated the rates of Saci-induced SN and FN and the associated demographic and clinical factors, as well as G-CSF use and total cost. Methods: This was a single-center retrospective analysis conducted at the University of Chicago. A total of 87 pts aged ≥18 who received Saci for advanced TNBC or HR+/HER2- breast cancer from 04/2020-09/2024 were eligible; of which, 77 without primary G-CSF prophylaxis were analyzed. We compared the rates of SN and FN to the landmark phase III trials: ASCENT and TROPiCS-02. Summary statistics were used to describe G-CSF utilization and cost. We performed multivariable logistic regression to examine factors associated with SN and FN. Results: Of 77 pts (59 TNBC and 18 HR+/HER2- tumors), the mean age was 56 years; 49% were White, 36% Black, and 14% Other. Overall, 38 (49%) pts had SN, and 3 (4%) had FN. In TNBC, the rates of SN (49% vs 51%; p = .78) and FN (5% vs 6%; p = .95) were similar compared to the ASCENT trial. For HR+/HER2- breast cancer, SN (50% vs 51%; p = .95) and FN (0 vs 5%; p = 1.00) rates were also comparable to the TROPiCS-02 trial. The SN rate was higher in Black pts than in White pts (61% vs 53%; p = .01); however, this racial difference was not significant (adjusted odds ratio [AOR] 1.58, 95% CI: 0.51-4.90; p = .43), after controlling for demographic and clinical factors. Patients in the “Other” group had lower odds of SN than White pts (AOR 0.08, 95% CI: 0.01-0.78; p = .03). HR+/HER2- tumors, 3+ prior lines of myelosuppressive chemotherapy, full starting dose, and baseline ANC > 50% quartile were associated with greater odds of SN, though not statistically significant due to the small sample size. Additionally, 62 out of 87 pts (71%) received G-CSF as primary or secondary prophylaxis, and the total G-CSF cost during the study period was $2.1 million. Conclusions: In this single-center analysis, we found similar rates of Saci-induced SN and FN in pts with metastatic TNBC or HR+/HER2- breast cancer compared to large clinical trials. Our study also revealed racial and clinical differences in SN and high G-CSF cost, suggesting high-risk subgroups to decrease these disparities. Given our limited sample, larger studies are needed to confirm our findings.