New response evaluation criteria using early morphological change in imatinib treatment for patients with gastrointestinal stromal tumor.

Background: The introduction of molecularly targeted drugs, including imatinib, has greatly improved the prognosis of gastrointestinal stromal tumor (GIST), and based on the different response image, the methods of response evaluation have been established for GISTs. Furthrmore, the best response evaluation using them has been reported to be associated with progression-free survival (PFS) in imatinib treatment. However, since it is more important to predict the clinical outcomes of imatinib treatment in "early treatment phase", new predicting factor in earlier stage is desired to work out the whole strategy of each patient. Early morphological change (EMC) was previously reported as a predictive marker for molecularly targeted drugs in metastatic colorectal cancer. The purpose of the present study was to verify the efficacy of EMC in predicting the outcome in patients with GIST receiving imatinib at early evaluation.

Methods: We retrospectively reviewed 66 patients. EMC in computed tomography (CT) image was evaluated, and the patients were categorized into two groups: active MR (morphological response) (+) group and active MR (-) group. We investigated the association between the presence of active MR and clinical outcomes.

Results: Forty-five patients had active MR ( +). The median progression-free survival (PFS) in patients with/without active MR was 49/23 months (P = 0.0039).

Conclusion: The evaluation criteria based on EMC could be a sensitive method to predict the clinical outcome of imatinib treatment for patients with unresectable GIST.