People with cancer who are being treated with antineoplastic agents should undergo routine testing for thyroid abnormalities, as these medications are associated with thyroid dysfunction in 20% to 50% or more of these patients.

The newer antineoplastic agents (such as immunotherapies and targeted therapies specifically zeroing in the signaling pathways in cancer cells) that are linked with thyroid problems include tyrosine kinase inhibitors, bexarotene, radioiodine-based cancer therapies, denileukin diftitox, alemtuzumab, interferon-alpha, interleukin-2, ipilimumab, tremelimumab, thalidomide, and lenalidomide. A recent literature review of the thyroid-related side effects of these treatments revealed that underdiagnosis of thyroid dysfunction can have important consequences for cancer patient management, according to the investigative team, which was led by Ole-Petter Riksfjord Hamnvik, MB, BCh, BAO, MRCPI, of the Division of Endocrinology, Diabetes, and Hypertension in the Department of Medicine at Brigham and Women’s Hospital in Boston, Massachusetts.

As Hamnvik’s group notes in the Journal of the National Cancer Institute, clinicians may overlook drug-induced thyroid dysfunction because of the complexity of the clinical picture in such patients. The investigators found that symptoms of hypothyroidism such as fatigue, weakness, depression, memory loss, cold intolerance, and cardiovascular effects may be incorrectly attributed to the primary disease or to the antineoplastic agent. Such symptoms can lead to dose reductions of potentially life-saving therapies. In addition, hypothyroidism can alter the kinetecs and clearance of medications, leading to undesirable side effects. The patient’s quality of life may also be adversely affected. In some cases, thyroid disease may also indicate a higher likelihood of tumor response to the agent.

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Specific tests make hypothyroidism and thyrotoxicosis easy and inexpensive to diagnose, and treatment is straightforward. Therefore, Hamnvik and colleagues suggest that persons who are receiving antineoplastic agents be tested regularly for thyroid abnormalities.