Hypomagnesemia, or reduced magnesium levels, is a side effect of Erbitux® (cetuximab) treatment. Patients with colorectal cancer whose blood magnesium dropped the fastest also had the best response to Erbitux given with Camptosar® (irinotecan) .
Italian researchers measured magnesium levels for 68 patients before treatment began and then 6 hours, 1 7, 14, 21, 50, and 92 days later. After the seventh day, readings decreased consistently.
Magnesium levels fell at least 20 percent for 25 patients by the third week. More of these patients responded to treatment, they lived longer before their cancer got worse and had longer overall survival.
Response rates for patients with an early reduction in magnesium were 64 percent, compared to 25.6 percent of other patients.
Median time to progression for the early hypomagnesemia group was 6 months compared to 3.6 months for those whose magnesium levels fell more slowly. Overall survival was 10.7 months versus 8.9 months.
Measuring magnesium may provide a way to predict whether or not Erbitux will be successful in treating advanced colorectal cancer.
Bruno Vincenzi and colleagues wrote,
Our results confirm that cetuximab treatment may induce a reduction of Mg2+ circulating levels and offer the first evidence that Mg2+ reduction may represent a new predictive factor of efficacy in advanced colorectal cancer patients treated with cetuximab plus irinotecan.
SOURCE: Vincenzi et al., Clinical Cancer Research, Volume 14, Number 13, July 1, 2008.