Although we know that KRAS tumor mutations limit benefit from Erbitux, about six out of ten colorectal cancer patients have normal or wild type KRAS. Yet Erbitux doesn’t work for many of them either.
There may be a simple way to predict early in treatment whether Erbitux is going to help to not.
Significantly more patients whose blood levels of magnesium dropped more than 50 percent after their first treatment with irinotecan and Erbitux had their tumors shrink. It also took longer before their cancer got worse, and they lived longer.
Doctors in Italy measured magnesium levels in the blood of patients getting Erbitux and irinotecan for advanced colorectal cancer. All had previously gotten worse after standard therapy with oxaliplatin and irinotecan. Tests were done before treatment and 7, 14, 21, and 28 days later.
Comparing patients whose magnesium levels fell more than fifty percent (hypomagnesemia) to those whose didn’t:
- Median response rates were 55.8 percent in the hypomagnesemia group versus 16.7 percent in patients without it.
- Time to cancer progression was 6.3 months versus 3.6 months.
- Overall survival time was 11.0 months versus 8.1 months.
B. Vincenzi and the team in Rome concluded,
We have shown that early hypomagnesemia could be a predictor of efficacy and outcome in those patients. Magnesium circulating level is an easy and inexpensive biomarker to routinely be detected in patients treated with
Patients need to be aware that this was a small trial in less than 150 patients. Before depending on it to continue or stop treatment, studies with more patients are critical.
SOURCE: Vincenzi et al., Annals of Oncology,Advqnce Access,November 29, 2010.
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