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Early Magnesium Reduction in Advanced Colorectal Cancer Patients Treated with Cetuximab Plus Irinotecan as Predictive Factor of Efficacy and Outcome

Authors' Affiliations: Departments of ¹ Medical Oncology, ² Laboratory Medicine, and ³ Radiology, University Campus Bio-Medico, Rome, Italy; ⁴ Department of Surgical and Oncology Sciences, Section of Medical Oncology, Università di Palermo, Palermo, Italy; and ⁵ Medical Oncology and Integrated Therapies Unit, Policlinico Universitario G. Martino, Messina, Italy

Requests for reprints: Antonio Russo, Section of Medical Oncology, Department of Surgical and Oncology Sciences, Università di Palermo, Via del Vespro 127, 90127 Palermo, Italy. Phone: 39-091-6552500; Fax: 39-091-6554529; E-mail: lab-oncobiologia{at}usa.net.

Introduction: Magnesium plays a role in a large number of cellular metabolic reactions. Cetuximab is able to induce hypomagnesemia by interfering with magnesium (Mg²⁺) transport in the kidney. We designed this trial to investigate if Mg²⁺ 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 Mg²⁺ 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 Mg²⁺ 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 Mg²⁺ 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 Mg²⁺ group. The median time to progression was 6.0 versus 3.6 months in the reduced Mg²⁺ group and in that without reduction, respectively (P < 0.0001). Overall survival was longer in patients with Mg²⁺ reduction than in those without (10.7 versus 8.9 months).

Conclusions: 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.