[Analysis of imatinib trough concentration at steady state in adjuvant therapy of patients with high risk gastrointestinal stromal tumor].

Objective: To explore the features of imatinib mesylate (IM) plasma concentration during adjuvant therapy and clinical factors associated with IM plasma concentration in patients with high risk gastrointestinal stromal tumors (GIST), and to determine whether IM plasma concentration <1100 μg/L influences the efficacy of adjuvant therapy. Methods: A retrospective case control study method was used. Case inclusion criteria: (1) complete resection of lesion and GIST confirmed by pathology; (2) high risk classified according to modified National Institutes of Health classification system (2008); (3) administration of IM 400 mg/d for at least 1 month; (4) not taking the medication likely affecting IM pharmacokinetic, such as rifampicin, dilantin, and carbamazepine, within 1 month before blood collection. Data of GIST patients who visited GIST Disease - Oriented Outpatient, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology between January 2015 to December 2018 were retrospectively analyzed. After taking IM for 22-26 hours, 5 ml of peripheral venous blood was collected into EDTA anticoagulant tube. IM plasma concentration was detected by using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Patients were divided into <1100 μg/L group and ≥1100 μg/L group according to plasma concentration. Linear regression was used to analyze the relevance between clinical features and IM plasma concentration. Parameters with normal distribution were analyzed by Pearson correlation coefficient, and parameters with non-normal distribution were analyzed by Spearman correlation. Kaplan-Meier survival curves and COX regression model were used for survival analysis. Results: Among the 85 patients enrolled in the study, 49 patients (57.6%) were male and 36 (42.4%) were female, with mean age of (51.9±11.0) years. The body mass index was (22.5±2.9) kg/m(2) and body surface area was (1.6±0.2) m(2). Thirty patients received gene test, including 23 patients with c-Kit exon 11 mutation, 4 with c-Kit exon 9 mutation, 1 with c-Kit exon 11 and 17 mutation and 2 without c-Kit or PDGFRA gene mutation. The mean IM plasma concentration was (1391.4±631.3) μg/L, and there were 32 patients with plasma concentration <1100 μg/L and 53 patients with plasma concentration ≥1100 μg/L. There were no statistically significant differences between the two groups in gender, age, body mass index, body surface area, hematological examination (white blood cells, albumin, alanine aminotransferase, aspartate aminotransferase and serum creatinine), tumor location, tumor size, mitotic counts, duration of adjuvant therapy and methods of operation (all P>0.05). Positive correlation between IM plasma concentration and serum creatinine was observed in linear regression analysis (r=0.297, P=0.007), but there were no correlations between IM plasma concentration and age (r=0.044, P=0.686), body mass index (r=0.066, P=0.547), body surface area (r=-0.010, P=0.924), white blood cells (r=-0.080, P=0.478), albumin (r=-0.065, P=0.563), alanine aminotransferase (r=0.114, P=0.308), aspartate aminotransferase (r=0.170, P=0.127) and duration of adjuvant therapy (ρ=0.060, P=0.586). There was no statistically significant difference in IM plasma concentration between patients with different genders (t=0.336, P=0.738) and patients with different surgical methods (F=0.888, P=0.451). Up to March 1, 2019. the median follow-up time was 30 (range 4-49) months. Tumor recurrence was detected in two patients with plasma concentration <1100 μg/L and two with plasma concentration ≥1100 μg/L. One recurrent patient with plasma concentration <1100 μg/L was detected to harbor c-Kit exon 11 and exon 17 mutations, and the other did not receive gene detection. Two recurrent patients with plasma concentration ≥1100 μg/L were both detected to harbor c-Kit exon 9 mutation. The 3-year relapse-free survival rate was 96.4% in the cohort, 96.2% in patients with plasma concentration <1100 μg/L, and 96.6% in patients with plasma concentration ≥1100 μg/L. No significant difference in relapse-free survival was observed between the two groups (P=0.204). Univariate Cox analysis showed that IM plasma concentration <1100 μg/L was not a risk factor for patients with high risk GIST (HR=0.238, 95% CI: 0.022-2.637, P=0.242). Conclusions: IM plasma concentration of adjuvant therapy in patients with high risk GIST varies with individual. Patients with higher level of serum creatinine are more likely to have a higher plasma concentration. A blood drug concentration standard of less than 1100 μg/L for advanced GIST patients may not influence the prognosis of patients with high risk GIST.