Serial monitoring of imatinib pharmacokinetics (PK) in perioperative imatinib treatment in patients (pts) with gastrointestinal stromal tumors (GISTs): Results from the multinational phase II trial.

118Background: Imatinib plasma levels may be affected by the duration of exposure to imatinib and resection of the stomach. Therefore, we performed PK study to monitor imatinib plasma levels serially in the multinational phase II trial of perioperative imatinib for pts with large ( ≥ 10 cm) gastric GISTs without distant metastasis. Methods: In this trial conducted in Japan and Korea, 53 pts received neoadjuvant imatinib 400 mg daily and 40 pts received adjuvant imatinib after surgery. Blood samples for imatinib trough levels (Cmin) were collected after 1, 3, 6 months of each neoadjuvant and adjuvant imatinib and measured by using liquid chromatography-tandem mass spectrometry. For the comparison of imatinib Cmin between different time points, values were dose-adjusted and log-transformed. Results: During the neoadjuvant treatment, imatinib Cmin (mean ± standard deviation) was 2253.0 ± 1148.0 ng/mL (n = 49), 1623.3 ± 832.4 ng/mL (n = 47), and 1852.0 ± 1572.4 ng/mL (n = 45) after 1, 3, and 6 months of imati...