Treatment-Related Toxicity in Advanced MTC

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Unique side effects are associated with each drug approved to treat patients with metastatic medullary thyroid cancer (MTC). As antiangiogenic agents, both vandetanib and cabozantinib are associated with hypertension, diarrhea, intestinal perforations, and tracheal esophageal fistula, notes Steven I. Sherman, MD. These side effects should be managed closely, particularly since diarrhea is already associated with MTC.

There is a risk for QT interval prolongation for patients treated with vandetanib, points out Sherman. As a result, patients treated with this drug should be monitored closely by electrocardiogram. Additionally, vandetanib is associated with cutaneous side effects, mucositis, rash, and photosensitivity.

As a result of these toxicities, not all patients are candidates for treatment. For stable patients, active surveillance should be utilized, suggests R. Michael Tuttle, MD. However, for rapidly progressive disease, the benefits of aggressive treatment may outweigh the risks.

The final decision about whether to administer cabozantinib or vandetanib should include input from a multidisciplinary team and can be individualized based on the patient's preference, specifically in the case of borderline progressive and stable disease, notes Lori J. Wirth, MD. These drugs may be warranted, for patients with 2 cm metastatic lesions that grow by 25% of more over the course of a year, believes Sherman.