Outcome of patients with advanced GIST achieving a complete remission (CR) with imatinib (IM) before interruption: Pooled analysis of two consecutive prospective randomizations of the French Sarcoma Group BFR14 phase III trial

Abstract

10549 Background: Patients (pts) experiencing a major response under IM treatment seem to have a better outcome than others (Cioffi, ASCO 08). IM interruption in responding patients after 1 and 3 yrs of treatment results in a high risk of rapid progression after a few months. The influence of pattern of response on PFS before IM discontinuation is unknown. Methods: Since June 2002, 415 pts were included in this trial. Fifty-eight, 50 and 12 (ongoing) non progressive pts at 1, 3 and 5 yrs respectively were randomly offered to continue (C arm) or interrupt (I arm) IM. Sixty-four pts were randomized in the I arm, 32, 25 and 7 after 1, 3 and 5 yrs of IM treatment respectively. Time to progression (TTP) of pts achieving a CR or a major PR (residual tumor < 10mm) before IM interruption was compared to outcome of pts experiencing others patterns of response. Results: Twenty-three pts achieving a CR or a major PR (36%) before randomization in the I arm, 9 after 1 yr, 10 after 3 yrs and 4 after 5 yrs of IM treatment. As of December 2008, 15 relapses were observed in the CR group (65%) versus 36 in the other cohort of pts (90%). The median TTP were 10.5 months (IC95%: 9–16 months) for the CR group and 6.1 months (IC95%: 4–9.2 months) for the non CR group (p=0.058). The median TTP were 9.4 months for the CR group vs 6 months for pts randomized after 1 yr of treatment, 12.3 months versus 5.7 months for pts randomized after 3 yrs of treatment respectively. One third of pts achieving a CR before randomization in the I arm was free of disease in December 2008. Conclusions: A CR achieved under IM is not a prerequisite for a prolonged disease-free survival in advanced GIST after 1 or 3 yrs of treatment. Despite a trend for a favourable outcome, prognosis of pts with a CR or a major PR is similar to those achieving a PR or a disease stabilisation. A selected group of advanced GIST pts in CR could be cured with IM alone. New radiological assessments or response critera have to be implemented in order to define a real CR. [Table: see text]