INTRODUCTION:

Magnesium plays a role in a large number of cellular metabolic reactions. Cetuximab is able to induce hypomagnesemia by interfering with magnesium (Mg(2+)) transport in the kidney. We designed this trial to investigate if Mg(2+) serum level modifications may be related with clinical response and outcome in advanced colorectal cancer patients during treatment with cetuximab plus irinotecan.

EXPERIMENTAL DESIGN:

Sixty-eight heavily pretreated metastatic colorectal cancer patients were evaluated for Mg(2+) serum levels at the following time points: before; 6 hours; and 1, 7, 14, 21, 50, and 92 days after the start of treatment.

RESULTS:

Basal Mg(2+) median levels were significantly decreased just 7 days after the first anticancer infusion and progressively decreased from the 7th day onward, reaching the highest significance at the last time point (P < 0.0001). Twenty-five patients showed a reduction in median Mg(2+) circulating levels of at least 20% within the 3rd week after the first infusion. Patients with this reduction showed a response rate of 64.0% versus 25.6% in the nonreduced Mg(2+) group. The median time to progression was 6.0 versus 3.6 months in the reduced Mg(2+) group and in that without reduction, respectively (P < 0.0001). Overall survival was longer in patients with Mg(2+) reduction than in those without (10.7 versus 8.9 months).

CONCLUSIONS:

Our results confirm that cetuximab treatment may induce a reduction of Mg(2+) circulating levels and offer the first evidence that Mg(2+) reduction may represent a new predictive factor of efficacy in advanced colorectal cancer patients treated with cetuximab plus irinotecan.