Impact of serosal involvement/extramural growth on the risk of synchronous and metachronous peritoneal spread in gastrointestinal stromal tumors: proposal for a macroscopic classification of GIST

Background: Peritoneal and hepatic metastases are the main routes of spread of gastrointestinal stromal tumors (GIST). However, criteria to predict the site and pattern of recurrence in individual cases are still lacking. Patients: We retrospectively analyzed 67 consecutive GISTs with complete gross descriptions to correlate macroscopic patterns with clinical course. Primary endpoint was the appearance of synchronous or metachronous peritoneal disease. Tumors were classified into type I (luminal/intramural) and type II (extramural) based on the macroscopic/histologic presence or absence of normal tissue between deeper tumor border and serosa, respectively. Results: Patients were 35 men and 32 women (mean age, 64 yrs) with gastric (n=32), small bowel (n=30) and large bowel (n=5) GISTs. Based on the above proposal, 22 tumors were classified as type I and 45 as type II. Type I tumors were predominantly gastric (18/22; P<0.001) and frequently had very low/low risk (14/22; P<0.001) whereas type II tumors were predominantly intestinal (31/45; P<0.001) and often of intermediate/high risk (36/45; P