Prospective evaluation of prognostic factors for recurrence after complete surgical resection of gastrointestinal stromal tumors (GIST)

Abstract

10558 Background: The clinical course of GISTs can be highly variable, depending on their size, mitotic index and location. Imatinib has been effectively used to treat recurrent and metastatic GIST, but its role in the adjuvant setting is still evolving. Analyzing factors which predict recurrence will help identify subgroups of patients who will benefit the most from adjuvant imatinib therapy. Methods: We analyzed the following factors in a prospective series of patients with GIST: age, sex, location, size and mitotic index of the primary, recurrence rates and overall survival. Results: From April 1999 to May 2007, 37 patients with primary localized GIST who underwent complete surgical resection, were c KIT positive and received no adjuvant imatinib were evaluated and followed. Median age at diagnosis was 62 years (range 18-82 years); 59 % were females; median size was 5.5 cm (1.1- 19 cm) and the median duration of follow up was 37 months (7- 97 months). Stomach was the most common site of presentation (76 %) followed by small intestine (16 %) and colon (5 %). Seventeen (46 %) patients had tumors ≤ 5 cm, 10 (27 %) had tumors 5–10 cm and 10 (27 %) patients had tumors ≥ 10 cm. Twenty seven patients (73 %) had ≤ 5 mitosis/ 50 high power field (HPF), 3 patients (8 %) had 5–10 mitosis per 50 HPF and seven patients (19 %) had ≥ 10 mitosis per 50 HPF. Thirty of 37 (81 %) were free of recurrence and overall survival was 97 % (one patient in remission died of myocardial infarction). In patients who had a recurrence the median size of the tumor was 14 cm (range 5.5- 19 cm) and median duration from diagnosis to recurrence was 27 months (12- 65 months). Outcome data on recurrence rates is presented in the table with statistical comparison between the various groups studied. Conclusions: Patients presenting with GIST ≥ 10 cm, mitotic index ≥ 10 per 50 HPF or small intestine as their primary site remain at high risk for recurrence with long term follow up and would appear to be a subset which is more likely to benefit from adjuvant imatinib. Factors affecting recurrence rates in GIST Factor Recurrence N (%) No recurrence N (%) p value (Fisher’s exact test) Tumor size < 10 cm 1 (4%) 26 (96%) 0.0006 Tumor size ≥10 cm 6 (60%) 4 (40%) Primary site Stomach 3 (10%) 25 (90%) 0.0096 Primary site Small Intestine 4 (66%) 2 (33%) Mitosis < 10/50 HPF 0 (0%) 30 (100%) 0.00009 Mitosis ≥ 10/50 HPF 7 (100%) 0 (0%) N= Number of patients Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Novartis Novartis