To investigate imatinib plasma level and clinical features for Japanese patients undergoing long-term (≥ 2 years) imatinib therapy for gastrointestinal stromal tumors (GISTs) retrospectively.
Twenty-eight patients who received imatinib for a metastatic GISTs and continued radiological response (CR, PR and SD) for more than 2 years were enrolled. Bolld samples were collected 22-26 hours after the previous imatinib dose before the next scheduled dose and clinical data (sex, age, height, body weight, original and metastatic tumor site, history of gastrectomy, number of tablet and laboratory results) were collected in medical records.
Seventeen patients were male, and the median age and body surface index (BSA) were 65.5 years old and 1.579 m2, respectively. The number of patients who were taking 200, 300 and 400mg/day imatinib was one, 16 and 11, respectively. The median plasma level was 1131.5 ng/ml, and level of patients with gastrectomy were 902 ng/ml and ones without gastrectomy 1452.5 ng/ml (p = 0.0376, one side test). Plasma level of male was significantly low (p = 0.420, one side test). No other parameters were apparently correlated with imatinib plasma level. Every small BSA (≤1.53m2) patient required imatinib dose reduction to 200 or 300mg/day.
The effect factors of imatinib plasma level might be history of gastrectomy and sex, and small BSA patients may require the dose reduction of imatinib.
Clinical trial identification
All authors have declared no conflicts of interest.