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Stage IV and Recurrent Colon Cancer Treatment

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    Panitumumab

    Panitumumab is a fully humanized antibody against the EGFR. The U.S. Food and Drug Administration approved panitumumab for use in patients with metastatic colorectal cancer refractory to chemotherapy.[70] In clinical trials, panitumumab demonstrated efficacy as a single agent or in combination therapy, which was consistent with the effects on PFS and OS with cetuximab. There appears to be a consistent class effect.

    Evidence (panitumumab):

    1. In a phase III trial, patients with chemotherapy-refractory colorectal cancer were randomly assigned to panitumumab or best supportive care.
      • Patients receiving panitumumab experienced an improved PFS (8 weeks vs. 7.3 weeks, HR, 0.54; 95% CI, 0.44–0.66; P < .0001).[70][Level of evidence: 1iiDiii]
      • There was no difference in OS, which was thought to be the result of 76% of patients on best supportive care crossing over to panitumumab.
    2. In the PRIME (NCT00364013) study, 1,183 patients were randomly assigned to FOLFOX4 with or without panitumumab as first-line therapy for metastatic colorectal cancer.[71] The study was amended to enlarge the sample size to address patients with the KRAS wild-type tumors and patients with mutant KRAS tumors separately.
      • For patients with KRAS wild-type tumors, a statistically significant improvement in PFS was observed in those who received panitumumab/FOLFOX4 compared with those who received only FOLFOX4 (HR, 0.80; 95% CI, 0.66–0.97; P = .02, stratified log-rank test).[71][Level of evidence: 1iiDiii]
      • Median PFS was 9.6 months (95% CI, 9.2 months–11.1 months) for patients who received panitumumab/FOLFOX4 and 8.0 months (95% CI, 7.5 months–9.3 months) for patients who received FOLFOX4. OS was not significantly different between the groups (HR, 0.83; 95% CI, 0.67–1.02; P = .072).
      • For patients with mutant KRAS tumors, there was worse PFS with the addition of panitumumab (HR, 1.29; 95% CI, 1.04–1.62; P = .02, stratified log-rank test).
        • Median PFS was 7.3 months (95% CI, 6.3 months–8.0 months) for panitumumab/FOLFOX4 and 8.8 months (95% CI, 7.7 months–9.4 months) for FOLFOX4 alone.
    3. Similarly, the addition of panitumumab to a regimen of FOLFOX/bevacizumab resulted in a worse PFS and worse toxicity compared to a regimen of FOLFOX/bevacizumab alone in patients not selected for KRAS mutation in metastatic colon cancer (11.4 months vs. 10.0 months, HR, 1.27; 95% CI, 1.06–1.52).[72][Level of evidence: 1iiDiii]
    4. In another study (NCT00339183), patients with metastatic colorectal cancer who had already received a fluoropyrimidine regimen were randomly assigned to either FOLFIRI or FOLFIRI plus panitumumab.[73]
      • In a post hoc analysis, patients with KRAS wild-type tumors experienced a statistically significant PFS advantage (HR, 0.73; 95% CI, 0.59–0.90; P = .004, stratified log-rank).[73][Level of evidence: 1iiDiii]
        • Median PFS was 5.9 months (95% CI, 5.5 months–6.7 months) for panitumumab/FOLFIRI and 3.9 months (95% CI, 3.7 months–5.3 months) for FOLFIRI alone.
      • OS was not significantly different. Patients with mutant KRAS tumors experienced no benefit from the addition of panitumumab.
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