Thyroid carcinoma

Abstract

See also pages 401-2 and 553-9. The long term prognosis of patients with thyroid microcarcinoma is excellent: relapses occur in 3-5% of patients, and most of them are curable, whereas cancer-related death occurs among less than 1%. These data plead in favor of a conservative approach to initial therapy. Only retrospective studies are available to determine the optimal extent of initial therapy and to identify the few patients at risk of recurrence or even death due to their microcancer who should be treated more aggressively. A number of biases may have been introduced in these retrospective analyses. For instance, for patients in earlier studies who were treated mostly by lobectomy, L-thyroxine (LT4) treatment was frequently omitted, whereas more recently patients have often undergone bilateral thyroidectomy and thereafter have been treated with LT4 at a suppressive dose that is known to decrease the relapse rate. Few series have included active follow-up, as we did. This may be misleading because passive follow-up may cause the relapse rate to be underestimated. Moreover, clinical practice has changed over the years, and radioiodine ablation that was routinely performed in the early 1980s is now administered more selectively. The study of the 535 patients treated for microcarcinoma at the Mayo Clinic identified 2 independent prognostic indicators for relapse, namely, limited surgery (lobectomy) compared with more extensive surgery (near total thyroidectomy) and lymph node metastases. In our retrospective study, limited surgery (lobectomy) was also associated with an increased risk of relapse as well as multifocality, which was defined as the presence of more than two neoplastic foci at histologic examination. Multifocality and lymph node involvement were, in fact, significantly correlated in our series. Rare are the patients with thyroid microcarcinoma who initially present with extensive disease featuring clinical lymph node involvement or metastases at distant sites. The relatively high number of such patients in our series is simply because our institution is a major referral center, to which a high proportion of patients are sent for treatment of metastatic disease. These unusual cases were not taken into account in the statistical analysis. Near-total or total thyroidectomy compared with limited surgery reduces the recurrence rate. This is particularly evident in patients with multifocal disease. Near-total thyroidectomy is therefore advocated when the microcarcinoma is diagnosed before or during initial surgery, and it is preferably associated with dissection of the ipsilateral central compartment of the neck. If the microcarcinoma is diagnosed after initial surgery, the risks associated with a complete thyroidectomy should be weighed against the prospect of a low relapse rate before this radical procedure is indicated. The risk of relapse is particularly low in patients with a unifocal tumor and without lymph node involvement; it is even lower now, even after lobectomy with routine suppressive thyroxine treatment. The decision to perform a completion thyroidectomy will depend on what the clinician considers reasonable and above all what the patient prefers, especially when the remnant lobe is normal at ultrasonography. In our retrospective series, the number of patients who underwent radioactive iodine ablation was relatively high, and this can be attributed to the use of radioiodine for ablation in most thyroid carcinoma patients in the early 1980s. However, in a number of series of patients with differentiated thyroid carcinoma, radioiodine (RAI) ablation did not confer any benefit on patients with a tumor smaller than 1.5 cm or 1.0 cm in greatest dimension, and not even when lymph node metastases were present. This has led to a general consensus not to use RAI ablation routinely to treat these patients. Consequently, only patients with tumor spreading beyond the thyroid capsule, extensive lymph node involvement, or distant metastases are likely to benefit from RAI ablation. The subsequent management of patients treated for thyroid microcarcinoma is identical to that of low risk patients with a clinically palpable tumor: L-thyroxine treatment is given to reduce the thyroid-stimulating hormone (TSH) level to below 0.5 μU/mL, but total suppression of TSH secretion is not warranted. Clinical and ultrasonographic examinations are also performed annually with TSH and thyroglobulin determinations. A frequent cause for concern is the discovery at ultrasonography of micronodules in the remnant lobe after initial lobectomy. Such lesions appear in tandem with a detectable serum thyroglobulin level and are generally benign. However, fine-needle biopsy is indicated, when possible, when these micronodules increase in size, and complete thyroidectomy may ultimately prove mandatory. See editorial counterpoint on pages 401-2 and referenced original article on pages 553-9, this issue.