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Low-dose Imatinib Efficacy in a Gastrointestinal Stromal Tumor Patient With KIT Exon 11 W557_K558 Deletion
Hirotaka Suto1, Miyuki Kawamura2, Mitsunori Morita2
1Department of Medical Oncology, Hyogo Cancer Center, Akashi, Japan; hirotaka.suto@hyogo-cc.jp.
Background/Aim:
Gastrointestinal stromal tumors (GISTs) are rare cancers originating from Cajal's stromal cells in the gastrointestinal tract. The most common driver mutation in these cancers is the KIT mutation. This report presents a case of response to low-dose imatinib in a patient with GIST harboring KIT exon 11 W557_K558 deletion.
Case Report:
In June 2023, an 82-year-old male developed perineal pain. Computed tomography (CT) imaging revealed a mass measuring >9 cm, extending from the rectum to the prostate. Submucosal tumor biopsy revealed a tumor with CD117-positive and DOG1-positive spindle-shaped cells leading to a diagnosis of GIST. c-Kit gene mutation analysis detected a W557_K558 deletion in exon 11. Treatment with imatinib (400 mg/day) was initiated in late October 2023 to preserve organ function; the dose was reduced to 300 mg/day after 5 days of treatment and further reduced to 200 mg/day after 10 days, with continued treatment at this dose. The CT performed in January, April, and June 2024 showed that the rectal GIST had shrunk. The blood imatinib concentration remained at approximately 650 ng/ml from January to March 2024 and decreased to 391 ng/ml in May 2024.
Conclusion:
The response rate of GISTs to imatinib is influenced by genetic mutations. GIST with KIT exon 11 W557_K558 deletion is associated with a high risk of recurrence. In vitro data showed that low-dose imatinib was effective in such cases. Low-dose imatinib is a treatment option for patients with GIST harboring KIT exon 11 W557_K558 deletion who are intolerant to high-dose imatinib.
Insights
Low-dose imatinib effectively treated a gastrointestinal stromal tumor (GIST) with a KIT exon 11 mutation. This approach offers a viable option for patients with this specific GIST subtype who cannot tolerate standard doses.
Area of Science:
- Oncology
- Gastroenterology
- Genetics
Background:
- Gastrointestinal stromal tumors (GISTs) are rare mesenchymal neoplasms.
- KIT mutations, particularly in exon 11, are common drivers in GIST.
- This case focuses on a GIST with a specific KIT exon 11 W557_K558 deletion.
Purpose of the Study:
- To report a case of GIST treatment with low-dose imatinib.
- To evaluate the efficacy of low-dose imatinib in a patient with KIT exon 11 W557_K558 deletion.
- To highlight a potential treatment strategy for GIST patients intolerant to standard imatinib doses.
Main Methods:
- A case report of an 82-year-old male with rectal GIST and KIT exon 11 W557_K558 deletion.
- Treatment initiated with standard imatinib dose (400 mg/day) then reduced to 200 mg/day due to intolerance.
- Serial CT imaging and blood imatinib concentration monitoring.
Main Results:
- The patient's rectal GIST showed significant shrinkage on serial CT scans.
- Therapeutic blood imatinib levels were maintained at the reduced dose.
- The patient tolerated the low-dose imatinib regimen.
Conclusions:
- GIST response to imatinib is mutation-dependent.
- KIT exon 11 W557_K558 deletion is linked to a high recurrence risk.
- Low-dose imatinib is a feasible and effective treatment for GIST with this mutation in select patients.
