Impact of UGT1A1*28 Allele on the Safety and Effectiveness of Sacituzumab Govitecan in Metastatic Triple-Negative Breast Cancer: Real-World Evidence

Background: The UGT1A1 gene is associated with the toxicity caused by SN38, the cytotoxic component of Sacituzumab govitecan (SG) used in the treatment of metastatic triple-negative breast cancer (mTNBC), among other approved indications. In this study, we aimed to analyze the effect of UGT1A1*28 allele on the safety and, secondarily, the effectiveness of SG in mTNBC. Methods: This was a multicenter, ambispective study that included patients treated with SG for mTNBC. Genotyping for UGT1A1*28 was performed using real-time polymerase chain reaction (PCR). Adverse events (AEs) of grade ≥ 2 during the first three cycles were compared between patients who were homozygous mutant (UGT1A1*28/*28) and those with wild-type (WT) or heterozygous genotypes. Effectiveness between the two groups was also compared using progression-free survival (PFS) and overall survival (OS) assessed with the Kaplan–Meier method. Results: A total of 81 patients were included: 37.0% were WT, 55.6% heterozygous, and 7.4% homozygous mutant. All UGT1A1 *28/*28 patients experienced grade ≥ 2 AEs (100% vs. 69.3%; p = 0.109), with a statistically significant association in the case of febrile neutropenia (33.3% vs. 6.7%; p = 0.025), and a trend towards higher rates of anemia and diarrhea (50.0% vs. 17.3%; p = 0.053). Genotype did not influence PFS or OS; however, dose reductions were associated with better survival outcomes. Conclusions: This real-world study shows a correlation between toxicity and the presence of the UGT1A1*28 mutation in patients treated with SG for mTNBC. Improving treatment tolerability through dose reductions may enhance SG effectiveness. These findings support the implementation of UGT1A1 genotyping in routine clinical practice.