Hypothyroidism in patients with colorectal carcinoma treated with fluoropyrimidines.

Targeted therapy with tyrosine kinase inhibitors, including vascular endothelial growth factor receptors, has been demonstrated to induce hypothyroidism and thyroid dysfunction. Cancer patients with thyroid dysfunction may be underdiagnosed and undertreated. Thyroid function in colorectal cancer patients receiving fluoropyrimidine-based chemotherapy with or without bevacizumab was evaluated at baseline and monthly. In the present study, 3 of 27 (11.1%) patients who received fluoropyrimidine-based chemotherapy developed a thyroid-stimulating hormone (TSH) level >10 µU/ml, and 13 (48.1%) developed an elevation above the upper limit of the normal range. No difference in TSH elevation was noted between the bevacizumab and chemotherapy-alone group (50 vs. 45%; P=1.00, respectively). Three (11.1%) patients developed a TSH level >10 µU/ml and 2 with hypothyroidism were treated with thyroid hormone replacement therapy. We demonstrated that bevacizumab does not affect thyroid function but fluoropyrimidines may induce thyroid dysfunction in patients with colorectal cancer. Further investigation is required to clarify the mechanism of fluoropyrimidine-induced thyroid dysfunction.