Case Author(s): Yonglin Pu, M.D.,Ph.D.,Barry A. Siegel,M.D. , 06/02/2002 . Rating: #D3, #Q4

Diagnosis: Gastrointestinal Stromal Tumor (GIST)

Brief history:

55-year-old man who presented with a three-month history of upper abdominal fullness, weakness and anemia.


Whole-body Tumor PET Imaging

View main image(pt) in a separate image viewer

View second image(ct). Abdominal CT

View third image(pt). Whole-body Tumor PET Imaging 6 months after with imatinib mesylate (Gleevec)

Full history/Diagnosis is available below

Diagnosis: Gastrointestinal Stromal Tumor (GIST)

Full history:

55-year-old man presented with a three-month history of upper abdominal fullness, weakness, and anemia. A gastrointestinal stromal tumor (GIST) was diagnosed by endoscopic biopsy of a gastric mass. A CT scan done at an outside Hospital on 9-24-01 demonstrates multiple metastatic lesions in the liver.The patient is scheduled to undergo treatment with imatinib mesylate (Gleevec). This study is done to evaluate the extent of disease.


15.0 mCi F-18 Fluorodeoxyglucose


There are multiple foci of increased FDG uptake throughout the liver. The largest one in the posterior segment of the right lobe of the liver demonstrates centrally absent activity consistent with massive central necrosis. Less extensive central necrosis is seen in the other hepatic lesions. These findings correlate with the CT findings of multiple hepatic metastases. There is a large focus of increased uptake of FDG in the region of the gastric fundus, which corresponds to the patient's known tumor.

There was a marked response to therapy with dramatic improvement in the FDG uptake in the gastric fundal mass as well as significantly decreased activity within multiple hepatic lesions (corresponding to cystic lesions seen on the CT scan obtained following Gleevec treatment). Mild activity persists within the gastric wall, with a few foci of increased activity in the liver just right of midline, likely corresponding to residual disease.


Gastrointestinal stromal tumors (GISTs) occur predominantly in middle-aged and elderly patients. About 70% of the tumors arise in the stomach and 20% to 30% of the tumors arise from the small intestine. The remaining tumors occur elsewhere in the gastrointestinal tract, or in the omentum or retroperitoneum. The tumors tend to be intramural, involving the submucosa and musclularis propria in continuity, and can extend to the mesentery and subserosa. GISTs can be single or multiple. Multifocal tumors are seen in Carney’s triad or neurofibromatosis.

Histologically, the tumor can be composed of spindle cells, epithelioid cells, or a mixed cell population.

These tumors are characterized by mutations of the KIT proto-oncogene that lead to constitutive activation of its tyrosine kinase activity. This can, in turn, stimulate the proliferation of the GIST cells and may inhibit apoptosis. The KIT protein (CD117) can be detected by an immunohistochemical method, which enable pathologists to distinguish GISTs from other mesenchymal gastrointestinal tumors (1).

Imatinib mesylate, (Gleevec, also called STI571) is an FDA-approved drug used for the treatment of chronic myeloid leukemia and GIST. It is a tyrosine kinase inhibitor. The experience with this drug in the treatment of GISTs is very encouraging. Within 8 hours of initiating Gleevec therapy, changes in the tumors can be seen on FDG-PET, suggesting a rapid metabolic response in the tumor cells. Histological examination demonstrates that the some of the tumors undergo myxomatous change,leaving small pyknotic nuclei in an eosinophilic myxoid background after treatment(1-2).

This case demonstrate that Gleevec is very effective in the treatment of GISTs and that its effect can be monitored by FDG-PET.

1. Berman JJ, O'Leary TJ. Gastrointestinal Stromal Tumor (GIST) Workshop, April 2 and 3, 2001, NIH, Bethesda, MD. Gastrointestinal stromal tumor workshop. Human Pathology 2001;32:578-582.

2. Joensuu H, Roberts PJ, Sarlomo-Rikala M, et al. Effect of the tyrosine kinase inhibitor STI571 in a patient with a metastatic gastrointestinal stromal tumor. N Eng J Med. 2001; 344:1052-6.


A gastrointestinal stromal tumor was diagnosed by biopsy of a gastric tumor.

View followup image(ct). Whole-body Tumor PET Imaging after therapy with Gleevec, 400 mg/day, for 6 months

Major teaching point(s):

Gastrointestinal stromal tumors (GISTs)are characterized by expression of KIT protein (CD117)and can be treated effectively with imatinib mesylate (Gleevec). FDG-PET can be used to monitor the therapeutic response.

Differential Diagnosis List

Gastric carcinoma, lymphoma, or leiomyosarcoma

ACR Codes and Keywords:

References and General Discussion of PET Tumor Imaging Studies (Anatomic field:Gasterointestinal System, Category:Neoplasm, Neoplastic-like condition)

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Case number: pt076

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