French scientists have validated a previous study that showed patients with a mutation in a the KRAS gene have little or no response to Erbitux (cetuximab).
The current research studied 89 patients who received Erbitux® after treatment with Camptosar® (irinotecan) had failed. Some were treated with Erbitux alone, some with a combination of Erbitux and Camptosar.
A KRAS mutation was present in about 30 percent of patients. Comparing those patients with the group that did not have changes in the KRAS gene, the researchers found:
- No reduction in the size of tumors (response) in the KRAS-mutated group versus a response to treatment that reduced tumor size in 40 percent of the non-mutated patients.
- Shorter time to tumors growing or appearing in new places (time to progression): 10.1 weeks in the KRAS-mutated group versus 31.4 weeks in the others.
- Shorter overall survival: 10.1 versus 14.3 months.
Severe skin rash has also been previously shown associated with survival after Erbitux treatment. The French team pooled the 89 patients in this study with their previous 30 patients to compare KRAS mutation to skin rash. While severe skin rash did predict longer overall survival independently, it was not a factor in either response to treatment or progression free survival.
Looking at the two favorable predictors of overall survival (severe skin rash and lack of a KRAS mutation) they found that median survival time was:
- Two predictors (severe rash and no KRAS mutation) 15.6 months.
- One predictor: (severe rash or no KRAS mutation) 10.7 months
- No predictors: (KRAS mutation without severe rash) 5.6 months
Writing about the importance of identifying those patients who will actually benefit from treatment with Erbitux, the authors said,
It is necessary to better define the subpopulation of patients who truly benefit from cetuximab because cetuximab is associated with an increase in treatment costs, frequent trips to therapeutic centers, and specific toxicity. Therefore, the identification of markers
allowing the selection of patients who are likely to benefit from this novel targeted therapy is an important challenge
Although Erbitux inhibits the activity of EGFR (epidermal growth factor receptors) on the surface of cancer cells reducing their ability to divide and grow, measurement of the level of EGFR in tumors using a common immunohistochemical test has not shown that lack of EGFR in tumors limits response to Erbitux. Patients whose tests show no EGFR can still respond to and benefit from treatment with Erbitux.
However, the current study, along with the previous one, show that testing tumors for a mutated KRAS gene does predict response, time to progression, and overall survival. It is a test that can be done before beginning treatment and can save patients from the cost and toxicity of a therapy that won’t benefit them.
The research team, led by Astrid Lievre, concluded,
These results confirm the high prognostic value of KRAS mutations on response to cetuximab and survival in metastatic CRC patients treated with cetuximab.
SOURCE: Lievre et al. Journal of Clinical Oncology, Volume 26, Number 3, January 20, 2008.
Previously, C3 News and Events carried a story about the earlier research.
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