Introduction: There are known correlations between axitinib exposure and treatment response. The aim of the article was to study relationships between the axitinib steady-state trough concentration and the treatment efficacy and toxicity.
Patients and methods: 35 patients (24 men and 11 women), treated or initiating treatment with axitinib, were included in the study over the period 2016-2019. Blood samples were collected following 2 weeks of treatment (in patients who initiated the therapy) and at the end of Cycles 1, 2, and 3 thereafter (in the entire study population). For concentration measurements, high-performance liquid chromatography - mass spectrometry (HPLC-MS) was applied. Treatment efficacy was assessed according to the RECIST 1.1 criteria. Therapy toxicity was evaluated according to the CTCAE criteria.
Results: A statistically significant relationship between the first measured axitinib trough concentration (Ctrough first) value and treatment response (P = .004) as well as the median progression-free survival (mPFS) (P = .003) was observed. The association between axitinib Ctrough first and the median overall survival (mOS) was not statistically significant (P = .142). A statistically significant relationship was observed between the mean trough concentration from 3-month observation (Ctrough 1-3m) and treatment response (P = .008) as well as mPFS (P = .001), without a significant relationship for mOS (P = .097). At least grade 3 adverse reactions were meaningfully associated with Ctrough first (P = .012) and Ctrough 1-3m (P = .003).
Conclusion: There are significant relationships between axitinib Ctrough and treatment response, PFS, and grade ≥ 3 toxicity. The data collected may be used to determine indications for axitinib therapy monitoring based on Ctrough measurements.
Keywords: Therapeutic drug monitoring; Treatment efficacy; Treatment safety; Trough level; Tyrosine kinase inhibitors.
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