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.

backgroundPeritoneal 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.

resultsPatients 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<0.001). Ten patients had synchronous peritoneal spread and 6/30 patients with a mean follow-up of 29 months developed metachronous peritoneal spread at a mean of 27 months. Tumor rupture was seen in 2 patients (3%). Thus, 16/40 patients (40%) had synchronous or metachronous peritoneal progression. Taken by gross type, peritoneal progression was seen in 15/30 type II compared to 1/10 type I tumors (p=0.032).

conclusionthis study points to extramural growth as a predictor of peritoneal recurrence in GIST, probably as a consequence of tumor rupture or due to microscopic serosal penetration. This study aimed at alerting surgical pathologists to the importance of careful gross and microscopic assessment of resection specimen harboring GIST to allow for reliable prospective evaluation of serosal involvement as an adverse prognostic factor in GIST.