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Updated: Apr 27, 2026
Robotic Duodenal Sleeve Resection for Gastrointestinal Stromal Tumor with Rare Exon 8 KIT Mutation Following Neoadjuvant Imatinib
Published on: April 3, 2026
Novel somatic KIT exon 8 mutation with dramatic response to imatinib in a patient with mucosal melanoma: a case
Suthee Rapisuwon1, Kellie Parks, Waddah Al-Refaie
1aDivision of Hematology/Oncology, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center bMelanoma Disease Group, Medstar-Georgetown Cancer Network, Washington, District of Columbia cDivision of Surgical Oncology, Medstar-Georgetown University Hospital, USA.
Abstract:
Primary mucosal melanomas represent ∼1.3% of all cases of melanoma diagnosed in the USA. The sinonasal location is the most common primary site. Mutations in the KIT gene occur in 10-22% of mucosal melanomas. Tumor response to imatinib mesylate has been reported in about half of the patients with tumors harboring KIT mutations. Responses are almost exclusively restricted to tumors with mutations in KIT exon 9 or 11. We report a case of a patient with a sinonasal mucosal melanoma with a novel exon 8 mutation (C443S) who had marked initial response to imatinib. Somatic exon 8 KIT mutations have not been previously reported in mucosal melanoma or in other human solid tumors; however, such mutations have been reported in canine and feline mast cell tumors. Protein transcripts from exon 8 play an important role in the structural and functional integrity of the extracellular domain of KIT. In preclinical studies, a mutation in exon 8 led to autophosphorylation, independent of KIT ligand, and constitutive activation of the tyrosine kinase. This biology may explain the successful application of imatinib in animals with tumors harboring exon 8 KIT mutations and in our patient with mucosal melanoma. This report expands the population of patients with melanoma who might benefit from imatinib to those with somatic exon 8 KIT mutations. Such mutations should be looked for in patients with mucosal melanoma.
Insights
A novel KIT exon 8 mutation in sinonasal mucosal melanoma responded to imatinib. This finding expands imatinib eligibility to patients with this rare KIT mutation.
Area of Science:
- Oncology
- Genetics
- Pharmacology
Background:
- Mucosal melanomas, rare cancers primarily affecting the sinonasal tract, often harbor KIT gene mutations.
- KIT mutations in exons 9 and 11 are linked to imatinib response in some patients.
- The role of other KIT mutations, such as in exon 8, remains largely unexplored in mucosal melanoma.
Observation:
- A patient with sinonasal mucosal melanoma presented with a previously unreported somatic mutation in KIT exon 8 (C443S).
- This patient demonstrated a significant initial response to imatinib mesylate treatment.
- Exon 8 mutations in KIT are associated with constitutive tyrosine kinase activation, similar to findings in canine and feline mast cell tumors.
Findings:
- This case report details the first instance of a somatic exon 8 KIT mutation in human mucosal melanoma.
- The observed clinical response to imatinib suggests therapeutic potential for this mutation type.
- Preclinical data supports the mechanism of imatinib efficacy in tumors with exon 8 KIT mutations due to constitutive kinase activation.
Implications:
- This study broadens the scope of patients who may benefit from imatinib therapy to include those with sinonasal mucosal melanoma harboring specific exon 8 KIT mutations.
- Routine screening for somatic exon 8 KIT mutations in mucosal melanoma patients is recommended to identify potential candidates for imatinib treatment.
- Further research into KIT exon 8 mutations could uncover new therapeutic strategies for rare cancers.
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