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RAS Status Predicts Response to Second-Line Treatment With Panitumumab for Metastatic Colorectal Cancer

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Key Points

  • Eighteen percent of patients already known to have no mutations at KRAS exon 2 harbored additional RAS mutations shown to predict clinical response to panitumumab treatment.
  • For patients in the mutated RAS group, the addition of panitumumab to FOLFIRI resulted in no significant survival differences over FOLFIRI alone
  • These findings may spare patients with RAS mutations the unnecessary costs and side effects of a treatment that will not improve their outcomes.

New data from a phase III clinical trial shows that patients with metastatic colorectal cancer tumors that contain RAS mutations beyond KRAS exon 2 are unlikely to benefit from the addition of panitumumab (Vectibix) to second-line FOLFIRI (leucovorin, fluorouracil, irinotecan) chemotherapy. Currently, doctors routinely test metastatic colorectal tumors for mutations in the KRAS gene at exon 2, which was previously shown to predict response to panitumumab treatment; however, the results of this study confirm the need to test for additional RAS mutations prior to administering panitumumab. The findings will be reported at the 2014 Gastrointestinal Cancers Symposium, held January 16 to 18 in San Francisco (Abstract LBA387).

“By testing for RAS mutations, doctors will be able to better select among metastatic colorectal cancer patients and only recommend panitumumab treatment to those who are most likely to benefit,” said lead study author Marc Peeters, MD, PhD, Professor of Oncology at Antwerp University Hospital in Edegem, Belgium. “These results confirm that it is RAS status that matters, not just KRAS, when determining if panitumumab therapy could be beneficial. For patients with a RAS mutation, these findings will spare them the costs and side effects of a treatment that will not improve their outcomes.”

Panitumumab is a fully human monoclonal antibody that blocks the epidermal growth factor receptor (EGFR), a protein known to promote the growth of colorectal cancer. Previous research has shown that EGFR inhibitors like panitumumab are not effective for colorectal tumors with mutations in the KRAS gene at exon 2, which occur in approximately 40% to 50% patients with metastatic colorectal cancer. More recent studies have identified additional genetic biomarkers in the RAS family of genes that predict clinical response to panitumumab, most notably mutations in KRAS and NRAS gene exons.

Phase III Study

In the present study, tumor samples from patients treated as part of a large, phase III study that were already known to be unmutated at KRAS exon 2 were assessed for other RAS mutations, specifically in KRAS exons 3 and 4 and NRAS exons 2, 3, and 4. The results indicate that 18% of these patients harbored one or more RAS mutations and that these mutations predicted clinical response to panitumumab treatment.

Among patients receiving both panitumumab and chemotherapy, both median overall survival and progression-free survival were improved for patients with wild-type RAS tumors compared to those with RAS mutations (median overall survival, 16.2 vs 11.8 months; median progression-free survival, 6.4 vs 4.8 months). For patients in the mutated RAS group, the addition of panitumumab to FOLFIRI resulted in no significant survival differences over FOLFIRI alone (median overall survival, 11.8 vs 11.1 months; median progression-free survival, 4.8 vs 4.0 months).

These findings support previously reported outcomes of panitumumab treatment based on RAS status in metastatic colorectal cancer and provide the first published phase III data in a second-line setting. In addition, the results, combined with those of other trials, support the use of more comprehensive RAS testing to identify specific subgroups of patients for whom panitumumab and other anti-EGFR treatment is appropriate.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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