Single agent panitumumab in KRAS wild-type metastatic colorectal cancer patients following cetuximab-based regimens: Clinical outcome and biomarkers of efficacy.

Background: Few data are available outlining outcomes of panitumumab in advanced colorectal cancer patients benefiting from prior cetuximab-based regimens.

Patients And Methods: Thirty patients with KRAS wild type metastatic colorectal cancer with clinical benefit from prior cetuximab-based regimens between May 2004 and October 2011 were reviewed at nine Italian Institutions. Inclusion key criteria included interruption of cetuximab for reasons other than progressive disease. Patients were classified according to prior regimens (0 or ≥1), prior response or stabilization, surgery of metastases, and Köhne prognostic score. At the time of subsequent progression, patients were treated with single agent panitumumab until progressive disease, unacceptable toxicity, or consent withdrawal.

Results: Panitumumab obtained 67% disease control rate and 30% objective response rate, with median PFS of 4.2 and median OS of 9.6 mo. Patients with BRAF/NRAS/PI3KCA and KRAS (by mutant enriched technique) wild-type tumors had the best chance of response to panitumumab.

Conclusions: Single agent panitumumab provided significant clinical benefit in heavily pretreated patients without acquired resistance to prior cetuximab-based regimens.