Magnetic Resonance Imaging as an Early Indicator of Clinical Outcome in Patients With Metastatic Colorectal Carcinoma Treated With Cetuximab or Panitumumab

PurposeThe early identification of patients with metastatic colorectal carcinoma who are likely to benefit from treatment with panitumumab or cetuximab remains of paramount importance. We evaluated whether the early tumor shrinkage assessed by magnetic resonance imaging (MRI) is predictive of long-term outcome to these epidermal growth factor receptor–targeted therapies.Patients and MethodsThirty-nine patients with chemorefractory metastatic colorectal carcinoma were treated with cetuximab or panitumumab. The patients were evaluated by unenhanced MRI at baseline, week 2, and week 8 after the beginning of the treatment and by contrast-enhanced computed tomography within 3 months. Early response was defined as a tumor shrinkage ≥10% at week-2 MRI, whereas response by contrast-enhanced computed tomography was defined according to standard Response Evaluation Criteria in Solid Tumors 1.1.ResultsAt week-2 MRI, 15 (38.5%) of 39 patients had an early response. Eleven (73.3%) of these 15 early responders then presented a partial response by contrast-enhanced computed tomography, whereas none of the 24 early nonresponders obtained a partial response (P < .0005, Fisher exact test). Median progression-free survival (PFS) was 29.7 and 8 weeks in patients with or without early response, respectively (hazard ratio [HR] 0.156 [95% CI, 0.069-0.355]; P < .0001)]. The median overall survival (OS) was 80 weeks in patients with early response and 23.3 weeks in those without early response, respectively (HR 0.154 [95% CI, 0.057-0.420]; P < .00005]).ConclusionsEarly detection of tumor response by week-2 MRI without contrast medium is associated with a prediction of clinical outcome in patients with metastatic colorectal carcinoma treated with cetuximab or panitumumab.