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Case Reports
. 2025 Jan-Feb;39(1):532-538.
doi: 10.21873/invivo.13857.

Low-dose Imatinib Efficacy in a Gastrointestinal Stromal Tumor Patient With KIT Exon 11 W557_K558 Deletion

Hirotaka Suto  1 , Miyuki Kawamura  2 , Mitsunori Morita  2 , Hideki Sakai  2 , Takuma Onoe  2 , Kyoko Ikeuchi  2 , Kazuyoshi Kajimoto  3 , Koji Matsumoto  2
Affiliations
Case Reports

Low-dose Imatinib Efficacy in a Gastrointestinal Stromal Tumor Patient With KIT Exon 11 W557_K558 Deletion

Hirotaka Suto et al. In Vivo. 2025 Jan-Feb.

Abstract

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.

Keywords: Gastrointestinal stromal tumor; exon 11 W557_K558 deletion; imatinib.

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Conflict of interest statement

KM has received research grants from Daiichi Sankyo, MSD, Eli Lilly, and Gilead Sciences (to institution); honoraria for lectures, presentations, speakers’ bureaus, manuscript writing, or educational events from MSD, Kyowa Kirin, Eli Lilly, Daiichi Sankyo, Eisai, and Chugai; advisory board fees from Gilead Sciences, Daiichi Sankyo, Pfizer, Genmab, Takeda, Eisai, and Nippon Shinyaku.

Figures

Figure 1
Figure 1
Histopathological examination of the rectal submucosal lesions. Hematoxylin and Eosin staining showing (A) a lesion with bundle-like proliferation of spindle-shaped cells and a slight presence of fibrous stroma around the lesion, ×100. (B) Lesions with bundle-like proliferation of spindle-shaped cells, ×400. Immunohistochemical staining showing (C) the expression of CD117, ×400 and (D) the expression of DOG1, ×400. (E) Ki67-positive cells (red arrows), comprising approximately 10%, ×400.
Figure 2
Figure 2
Computed tomography findings at the initial visit to our department for the patient with GIST. (A) Axial imaging of a giant mass with a short diameter of 54 mm in the rectum (red circle). (B) Sagittal imaging of partial invasion of the rectal mass into the bladder (red oval). (C) Coronal imaging of a giant mass 92 mm in length from the rectum to the bladder (red oval).
Figure 3
Figure 3
Course of treatment and changes in imatinib trough concentrations (Cmin) and serum creatinine levels (sCre).
See this image and copyright information in PMC

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