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Discussion

Neoplasms arising from the smooth muscle of the GI tract are uncommon, comprising only 1% of all tumors. Traditionally these tumors have been classified as leiomyomas or leiomyosarcomas, however, their origin and differentiation have been a source of controversy. As such, the term "gastrointestinal stromal tumor" was derived for such neoplasms, acknowledging uncertainties in behavior and phenotype. (1)

Lesions occur in all areas from the esophagus to the rectum with the stomach being the most common site. Forty-seven to 66% of these tumors are found in the stomach. Other sites in decreasing frequency are small bowel (19-35%), colorectal (2-12%), and esophagus (5-9%). (1)

In a collective review of the world literature from 1762 to 1996, 2189 pts were identified with benign GIST and 1594 pts with malignant GIST. The peak age of incidence of benign GIST was 50 to 59 years, while malignant GIST was 60 to 69. Women were more likely to develop benign lesions, and malignant lesions were more common in men. The most common sites of benign GISTs were on the anterior and posterior wall of the body and they typically grow intraluminally (endogastric); malignant GISTs were more common along the greater curvature and typically grow exogastric. (2)

The presenting symptoms of both types are similar; in decreasing order of frequency they were bleeding, pain, palpable mass, and weight loss. In several case series, GIB was the most common clinical feature, occurring in 40-65% of patients. Interestingly, there was no correlation between the size of the tumor and presenting signs or symptoms except patients with malignant GIST were more likely to have weight loss. (1)

The diagnostic yield of endoscopic biopsy, as one would expect, is poor (less than 50%) because samples are obtained from the overlying mucosa. Benign GISTs are frequently hypercellular, consisting of spindle-shaped or epithelioid cells that are often haphazardly grouped into bundles or fascicles. Mitotic figures are rare or absent. Benign lesions are commonly less than 5 cm in size. Malignant GISTs have bizarre nuclei, frequently with mitotic figures, and areas of necrosis. Tumors greater than 6 cm often belong to this group. The mitotic index remains the most useful and reproducible histologic criterion for malignancy, although metastases have been rarely reported even with tumors with few or absent mitotic figures.

These stromal tumors have an atypical immunohistochemical profile that can be used diagnostically. Markers that have been used include CD34, smooth muscle actin, and CD117.

Surgery remains the treatment of choice for GIST. Several reviews have found that tumors less than 5 cm can be adequately treated with wedge gastric resection with a margin of wall of 1-2 cm. No controlled study has documented efficacy for chemotherapy in the management of malignant GIST although newer agents are being evaluated.

Schiu et al, reported a 5-year survival of 32% for high grade GIST (greater than 10 mitoses per 10 HPF) and of 81% for low grade GIST (less than 10 mitoses per 10 HPF). (4)