Management of Papillary Thyroid Cancer Patients in Absence of Postoperative Radioiodine Remnant Ablation: Tailoring Follow-Up by Neck Sonography

Abstract

Throughout the world, small, differentiated thyroid cancers—papillary thyroid carcinomas (PTC) for the most part—are being diagnosed with growing frequency, an effect that can be attributed largely to technological advances in diagnostic imaging and greater diagnostic scrutiny (1). In most cases, the risk of disease recurrence and tumor-related mortality after total or near-total thyroidectomy appears to be quite low, and for this reason postoperative radioiodine remnant ablation (RRA) is being omitted in an increasingly large percentage of patients with PTC (2). This strategy, which tailors case management to individual risk levels, is in keeping with the 2009 American Thyroid Association (ATA) guidelines (3), which encourage more selective use of postoperative RRA. The challenge, however, is to find an effective approach for the postoperative follow-up of patients who have undergone total or near-total thyroidectomy without RRA. Although the outcome of these “low risk” PTC is almost invariably favorable, the patients still require regular, long-term surveillance. Indeed, persistent or recurrent disease can also occur in patients with early-stage tumors, and relapses have been reported as late as 10 yr after diagnosis (4). Effective postsurgical follow-up of patients thought to be disease-free should be capable of detecting recurrences: 1) early (when the chances of a cure are greatest); 2) with high sensitivity and specificity; and 3) with a high negative predictive value. Ideally, it should also allow us to identify—at some point—cases with a low enough likelihood of recurrence to justify less intensive surveillance, which would be not only more cost-effective but also easier on the patient (physically and psychologically). The 2009 ATA guidelines recommend that periodic serum thyroglobulin assay and neck ultrasonography (US) “be considered” during the follow-up of patients whose differentiated thyroid cancers have been managed with subtotal thyroidectomy or with total thyroidectomy not followed by RRA (recommendation 44) (3). However, little distinction is made between these two methods, and few details are offered on their respective merits or shortcomings and how and when each might be used. Serum thyroglobulin assays after exogenous or endogenous TSH stimulation are considered the mainstay cornerstone of postoperative surveillance programs for patients with PTC (3). Indeed, detectable TSH-stimulated thyroglobulin levels or increases over time in their values are a highly specific marker of residual/recurrent disease for patients treated with postoperative RRA (3, 5); until recently, this included virtually all of those who were treated for PTC. What we know about the diagnostic value of serum thyroglobulin assays is largely based on their performance in this population after TSH stimulation. But for patients who do notundergoRRA,theseassaysaremoredifficult to interpret. Detectable thyroglobulin production in these cases may well originate exclusively from the remnant of normal thyroid tissue leftafter surgery,andtheboundariesbetween“normal and neoplastic production” have never been specifically investigated in this population. Consequently, for a rapidly growing subset of PTC patients, serum thyroglobulin assays currently have some important limitations as postoperative follow-up tools. By contrast, neck sonography has a number of features that are valuable in the postoperative follow-up of PTC patients (5–8). Persistent or recurrent disease is almost always associated with spread to the cervical lymph nodes,