Marc Peeters, MD, PhD, department of oncology, Antwerp University Hospital, Antwerpen, Belgium, discusses the frequency of S492R
mutations found in patients with metastatic colorectal cancer who were treated with panitumumab or cetuximab monotherapy.
For this analysis, tumor samples from the phase III ASPECCT trial were analyzed to find the specific point mutation of S492R
in the EGFR receptor region, Peeters notes. In ASPECCT, the EGFR inhibitors panitumumab and cetuximab were compared as treatments for patients with chemorefractory wild-type KRAS metastatic colorectal cancer.
Researchers compared baseline results to tumor samples that were taken 4 weeks after treatment was stopped, in order to ascertain whether the mutation is due to induction of resistance or if it was already present at baseline, Peeter notes.
At baseline, S492R
mutations were not detected in either arm. However, following treatment, 16% of patients that were treated with cetuximab tested positive for the mutation compared with less than 5% in the panitumumab arm.
These findings highlight the differences between the two EGFR inhibitors. This analysis provides new insight for treatment strategies, Peeters believes, since patients who develop the S492R
mutation following induction therapy with cetuximab could potentially still be candidates for treatment with panitumumab.
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