Clinicopathologic study of 275 cases of gastrointestinal stromal tumors: the experience at 3 large medical centers in Mexico.

It is important to distinguish gastrointestinal (GI) stromal tumors (GISTs) from other GI mesenchymal tumors (GIMTs) because of the availability of molecular-targeted therapy for GISTs. The aim of the study was to reclassify GIMTs and to determine the clinicopathologic features of GISTs in Mexico. Cases of GIMT identified from the database of 3 large diagnostic centers in Mexico between 1995 and 2004 were reclassified according to current criteria. Hematoxylin and eosin-stained sections and clinical histories were reviewed, and immunohistochemistry was performed using anti-CD117, CD34, smooth muscle actin, and S-100 protein. A total of 275 GISTs were identified. The tumors were located in the stomach (40%), small intestine (35%), colorectum (12%), abdominal cavity (11%), and esophagus (2%). There were equal numbers of men and women with a mean age at diagnosis of 61 years. The tumors ranged in size from 3.5 to 34 cm (mean, 9.1 cm); 95 tumors (34%) were larger than 10 cm. Colorectal and omental tumors were the largest. The cell types included pure spindle (68%), pure epithelioid (16%), and mixed epithelioid/spindle (14%). Whereas 17.8% of tumors were regarded as low risk, 43% of tumors were in the high-risk category. CD117 positivity was detected in most of the tumors (96%). In addition to CD117, 255 cases (92%) were positive for CD34, 82 cases (32%) were positive for smooth muscle actin, and 13 cases (4.7%) were positive for desmin. Gastrointestinal stromal tumors in Mexico have the same clinicopathologic and immunohistochemical features as those reported in other countries. It is not always easy to distinguish GISTs from other soft tissue lesions. The diagnosis can be difficult even for experienced pathologists.