Relative Factors Analysis of Imatinib Trough Concentration in Chinese Patients with Gastrointestinal Stromal Tumor

Aims: Imatinib plasma trough levels (IM C min ) have been reported to have a considerable clinical impact in patients with gastrointestinal stromal tumors (GISTs). We therefore have investigated the factors affecting IM plasma concentration in Chinese GIST patients. Methods: IM C min in 190 patients with GIST who were taking IM were measured. Results: In patients treated with IM 300 mg/day (n = 16), 400 mg/day (n = 168), and > 400 mg/day (500: n = 1, 600: n = 5), IM C min was 1,564.54 ± 596.15, 1,521.26 ± 610.33, and 2,540.31 ± 1,298.14 ng/mL, respectively. Of the 168 patients treated with IM 400 mg/day, IM C min was significantly lower in males (1,353.94 ± 492.89 ng/mL) than in females (1,680.79 ± 669.03 ng/mL, p < 0.01), and in patients with gastrectomy (1,439.60 ± 587.66 ng/mL) than those without gastrectomy (1,649.88 ± 620.12 ng/mL) (p = 0.033). High IM C min was correlated with low body weight (p = 0.004) and low body surface area (p < 0.001). Conclusion: IM C min at steady state was significantly associated with body weight and body surface area. Monitoring of IM C min might be particularly important for the optimal treatment with IM of male patients and those who have undergone gastrectomy.