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.
Pazo-Oubiña et al. (Sat,) studied this question.