Imatinib for 3 years is the most appropriate adjuvant treatment for this patient, who has a localized gastrointestinal stromal tumor (GIST) associated with a relatively higher risk for recurrence. GISTs, although rare, are the most common sarcoma of the gastrointestinal tract. The most common site is in the stomach, but GISTs can arise anywhere in the digestive tract. Location outside the stomach, larger size, and higher mitotic index constitute relative high-risk factors for recurrence after resection. Patients with small gastric GISTs with low mitotic indices may often be managed with surgery alone. Higher-risk tumors, such as in this patient, require further treatment. A 3-year course of the oral tyrosine kinase inhibitor imatinib has been shown to improve outcomes when used as adjuvant therapy after surgical resection of localized higher-risk GISTs. Imatinib has also been shown to be highly active in treating patients with metastatic GISTs, in whom lifelong therapy is recommended. Finally, randomized clinical trials have shown a superior outcome for those patients with localized higher-risk GISTs who receive imatinib for 3 years compared with those receiving 1 year of treatment.

The MAGIC trial demonstrated the superiority of preoperative and postoperative chemotherapy (epirubicin, cisplatin, and 5-fluorouracil) compared with surgery alone for treatment of gastric and esophageal/gastroesophageal junction adenocarcinomas. In patients who undergo surgery as initial therapy, postoperative 5-fluorouracil and leucovorin plus radiation therapy have been shown to confer a survival benefit compared with postoperative observation alone. These therapies are not effective treatments for GISTs.

GISTs are relatively resistant to radiation, and adjuvant radiation therapy is not routinely indicated.

Observation following surgical resection is appropriate only for patients with GISTs associated with favorable risk factors, whereas this patient has a higher-risk tumor.