[Gastrointestinal stromal tumour (GIST): current standards in multimodal management]

Gastrointestinal stromal tumours (GIST) are the most frequent mesenchymal tumours of the gastrointestinal tract. The gold standard therapy is their complete surgical removal with safety margins of 1-2 cm. Intraoperative damage to the tumour must be avoided because tumour rupture carries a very high risk of peritoneal spread. Since metastases to lymph nodes in general does not occur in GIST a lymph node dissection is not indicated. Depending on the size of the tumour, the number of mitoses and the localisation of the primary tumour, the risk of recurrence after potentially curative resection is considerable in many cases. Patients with intermediate and high risk according to Miettinens classification should receive adjuvant treatment with imatinib. Exceptions are those patients whose tumours exhibit a mutation in exon 18, D842V of PDGFRA. According to current data the therapy is continued for 3 years. This leads not only to a significant improvement of the progression-free survival in comparison to therapy for 1 year but also, especially, to an improvement of overall survivial. In the case of local advanced tumours that can only be resected by a mutilation operation, a primary systemic therapy with imatinib should be initiated on account of its extremely high efficacy. Standard therapy for local advanced or metastasizing GIST is imatinib at a dose of 400 mg/day. Patients with mutations in KIT exon 9 should be treated with 800 mg imatinib/day, since they profit from a significantly longer progression-free survival. Therapy with imatinib should always be continued up to progression or intolerance. In the case of progression under 400 mg imatinib the ESMO guidelines recommend a dose increase to 800 mg/day as about a third of the patients respond to this higher dose. In the case of further progression a switch to second-line therapy with sunitinib is recommended. After exploitation of all registered therapy options the patients should be offered an experimental therapy within the framework of a clinical trial.

Twelve versus 36 months of adjuvant imatinib (IM) as treatment of operable GIST with a high risk of recurrence: Final results of a randomized trial (SSGXVIII/AIO)

LBA1

Background: Adjuvant IM administered for 12 months (mos) after surgery improves recurrence-free survival (RFS) of patients (pts) diagnosed with operable GIST. We compared 12 vs 36 mos of adjuvant IM as treatment of pts with a high risk for GIST recurrence after surgery. Methods: Pts with histologically diagnosed KIT-positive GIST were entered to this prospective, open-label, multicenter, randomized Phase III study (identifier NCT00116935 ). The risk of recurrence was estimated according to the modified Consensus Criteria. The primary objective was RFS. The secondary objectives included survival (OS) and treatment safety. The key exclusion criteria were ECOG PS >2, metastatic or inoperable GIST, and >12 wks from surgery to the study entry. IM was administered orally 400 mg/d. The sample size (n =200 in each group to obtain ≥110 events) was estimated by simulating log-rank tests assuming an overall hazard ratio (HR) of 0.44, a 20% drop-out rate, 2-sided type-I error rate of .05 and power 0.80. Analysis was based on the intention-to-treat population (ITT). Tumor histology was centrally reviewed. Results: 400 pts were entered to the study from Feb 2004 to Sep 2008. Three pts were excluded due to lack of consent from the ITT, which includes 15 pts who did not have GIST at a central review. The median FU time was 54 mos. RFS was longer in the 36-mo group compared to the 12-mo group (HR 0.46, 95% CI 0.32-0.65; p <.0001; 5-y RFS 65.6% vs 47.9%, respectively). Pts assigned to 36-mo of IM had longer OS (HR 0.45, 0.22-0.89; p =.019; 5-y OS 92.0% vs 81.7%). IM was generally well tolerated. The proportion of pts who discontinued IM during the assigned treatment period for reasons other than GIST recurrence was 25.8% in the 36-mo group and 12.6% in the 12-mo group. Exploratory efficacy subgroup analyses including KIT and PDGFRA mutation analysis data from 366 tumors will be presented. Conclusions: IM administered for 36 mos improves RFS and OS compared to 12 mos of administration as adjuvant treatment of GIST pts who have a high estimated risk of recurrence after surgery.