Papillary thyroid cancer: medical management and follow-up

Abstract

The incidence of epithelial derived thyroid cancer (papillary thyroid cancer and follicular thyroid cancer, known collectively as differentiated thyroid cancer) is rising. About 80% of patients with thyroid cancer have PTC and are best treated with thyroidectomy and functional lymph node dissection, followed by radioiodine ablation or therapy and performance of a posttreatment whole-body scan, followed by thyroid stimulating hormone (TSH) suppression. One year after radioiodine administration, the use of sensitive thyroglobulin (Tg) assays can separate the vast majority of patients with persistent disease from those who are free of disease and unlikely to have recurrent disease all without the need for repeat whole-body radioiodine imaging. Patients with detectable serum Tg during TSH suppression (Tg-on) or Tg that rises above 2 ng/mL after TSH stimulation (TSH-Tg) are highly likely to harbor residual tumor. TSH stimulation can be achieved using either thyroid hormone withdrawal or recombinant human TSH (rhTSH). Highly skilled screening neck ultrasonography can identify a few additional patients with subcentimeter residual neck lymph node metastases not detected by TSH-Tg. However, ultrasonography and chest computed tomography (CT) are most critical for tumor localization in those patients with Tg values that suggest residual disease or in those patients with persistent antithyroglobulin antibodies (TgAb) that falsely lower Tg measurement. TgAb quantitative titers typically resolve steadily over just a few years in patients free of disease after initial therapy. Another paradigm shift is the recognition that most patients who eventually achieve freedom from disease do so by surgery with fewer patients cured by repetitive radioiodine treatments, and even fewer cured with external beam radiation. Patients who appear to be free of disease require a lifetime of follow-up to optimize levothyroxine treatment, and they will undergo periodic stimulation testing because some will still manifest recurrent disease. Patients with persistent disease despite negative ultrasonography, chest CT, and whole-body radioiodine imaging may have a tumor identified by fluorodeoxyglucose positron emission tomography, optimally performed with combined TSH stimulation and image fusion with CT or magnetic resonance imaging. Patients with metastatic disease who are unresponsive to conventional treatment are encouraged to participate in increasingly available thyroid cancer-specific clinical trials using targeted experimental oral or intravenous chemotherapeutic agents to address this tumor that has historically proven resistant to conventional chemotherapeutic agents.