Gastrointestinal stromal tumor (GIST) is the most common soft tissue sarcoma of the gastrointestinal tract, usually arising from the interstitial cells of Cajal or similar cells in the outer wall of the gastrointestinal tract.1,2 Most GISTs have an activating mutation in KIT or platelet-derived growth factor receptor alpha (PDGFRα). Tumor size, mitotic rate, and anatomic site are the most common pathological features used to risk stratify GIST tumors.3-10 It is important to note when using such risk calculators that preoperative imatinib before determining tumor characteristics (such as mitoses per 50 high-power fields [hpf]) often changes the relevant parameters so that the same risk calculations may not apply. Tumors with a mitotic rate ≤5 mitoses per 50 hpf and a size ≤5 cm in greatest dimension have a lower recurrence rate after resection than tumors with a mitotic rate >5 mitoses per 50 hpf and a size >10 cm, and larger tumors can have a recurrence rate of up to 86%.11,12 Findings from a large observational study have suggested that the prognosis of gastric GIST in Korea and Japan may be more favorable compared with that in Western countries.13
The primary treatment of a localized primary GIST is surgical excision, but a cure is limited by recurrence.14,15 Imatinib is useful in the treatment of metastatic or recurrent GIST, and adjuvant treatment with imatinib after surgery has been shown to improve progression-free and overall survival in some cases.3,16-18 Responses to adjuvant imatinib depend on tumor sensitivity to the drug and the risk of recurrence. Drug sensitivity is largely dependent on the presence of mutations in KIT or PDGFRα.3,18 Recurrence risk is highly dependent on tumor size, tumor site, tumor rupture, and mitotic index.1,3,5,6,8,9,18,19 Findings on the use of gene expression patterns to predict recurrence risk have also been reported.20-27 However, recurrence risk is poorly understood for categories in which there are few cases with known outcomes, such as very small gastric GIST with a high mitotic index. For example, few cases of gastric GIST have been reported with a tumor size ≤2 cm, a mitotic rate >5 mitoses per 50 hpf, and adequate clinical follow-up. In such cases, it is difficult to assess the risk of recurrence.6 We report here the long-term outcome of a patient with a 1.8-cm gastric GIST with a mitotic index of 36 mitoses per 50 hpf and a KIT exon 11 mutation.