Imatinib-related toxicity profile in patients with gastrointestinal stromal tumors seen over a twenty-year period in Ile-Ife, Nigeria.

e23513 Background: The use of Imatinib mesylate in the first-line setting has changed the treatment landscape of GISTs. Imatinib mesylate-related toxicities have been widely reported in previous studies in other populations, but there is a paucity of data on the Nigerian population. Pharmacogenomic studies done in Nigerian patients have revealed remarkable unique differences in the metabolism of Imatinib mesylate, which may suggest different treatment outcomes and related toxicity profiles. It is unclear if Imatinib-related toxicities in the Nigerian population are different from what has been reported in other populations. We set out to investigate Imatinib treatment outcomes and related toxicity profile in Nigeria in patients with GISTs. Methods: This was a retrospective cohort study carried out at the Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC), Ile-Ife, Nigeria. Medical records of 135 patients diagnosed with GISTs from January 2003 to December 2023 were reviewed. The primary endpoint was the toxicity profile, and the secondary endpoint was the objective response rate. Grade of toxicity was assessed using the Common Terminology Criteria for Adverse Events (CTCAE) v 5.0, and objective response was evaluated using the RECIST criteria version 1.1. Descriptive statistics were used to summarize patient characteristics, treatment responses, and toxicity profiles. Results: Of all patients reviewed, 124 (96.9%) received standard first-line Imatinib at 400mg/day. One year after the commencement of Imatinib, four patients (3.1%) achieved a complete response, and 15 patients (11.5%) achieved a partial response to Imatinib treatment. Sixty-three patients (48.5%) had stable disease, and 13 patients (10.0%) had progressive disease. Most treatment-related toxicities were mild to moderate (80%), with the majority (77.6%) experiencing non-hematological toxicities, including peripheral oedema (44.7%) and hypopigmentation (35.6%). Neutropenia was the most common hematological toxicity (62.5%). Conclusions: Imatinib mesylate is a tolerable treatment option for patients with GISTs in Nigeria. Defaulting from regular clinic visits was the most common reason for poor drug adherence. The presence of a unique molecular mutation profile in Nigerian patients with GISTs may also have contributed to the observed low objective response rate.