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Mayo Clinic
Rochester, Minnesota
Stanford University Hospital and Clinics
Stanford, California
University of Michigan Health System
Ann Arbor, Michigan
REPLY: We appreciate Professor Bourgeois' thoughtful letter. Our perspective (1) was limited to making major points to indict ablation in the management of thyroid carcinomas, and Professor Bourgeois' questions offer an opportunity to expand on our thesis.
We agree with Professor Bourgeois that refinements in scintigraphic imaging will more accurately define the anatomic sites of residual functioning thyroid tissues. The sensitivity of imaging is also likely to improve over time. We further agree that diagnostic scintigraphic imaging may help to locate residual carcinomas and thereby aid in decisions about therapy (surgical or 131I). Although images made after ablation therapy may be more sensitive than pretherapeutic scans, we do not believe that this observation justifies such management of patients who have stage I carcinomas. If, from data available, there is concern about carcinoma not seen on the diagnostic images, consideration may be given to treatment, not ablation, with 131I. However, long-term benefits from this approach have not been shown. We also agree that if 131I treatments are to be given for carcinomas, the administered dose should be optimal, a goal that often requires dosimetry.
Whereas thyroglobulin antibodies often disappear over time after 131I ablation (2), it is possible that this immune interference may also disappear without radiation treatment. In any case, such antibodies may serve as a surrogate for circulating tumor thyroglobulin (3).
Because papillary microcarcinomas are so frequently present, the numbers of patients are difficult to grasp. From autopsy evidence, such tumors have been found in 1.4%–36% of populations around the world (4–6). In addition, of those afflicted, multifocality was found in 20%–47% and micrometastases to cervical lymph nodes in 3%–18% (4), yet cause-specific mortality was 0%–1% (6). Nevertheless, after surgical therapy, recurrences have been documented. For patients with primary tumors smaller than 5 mm, recurrences appear in about 1% (7). In follow-up, cervical metastases were discovered more frequently if, at the time of the original operation, the lymph nodes contained carcinoma (8,9). Hay et al. found that postoperative 131I treatments were not followed by statistically fewer nodal recurrences (8), but Chow et al. reported that, after ablation, new cervical disease was statistically less common (9). However, overall, recurrences in the absence of ablation therapy were seen in few patients: only 11 (8) and 4 (9).
Some patients with microcarcinomas may require therapy after surgical removal of the tumors; depending on ancillary findings, treatments will vary (6,10). Still, it is important to remember that the prognosis for most patients with microcarcinomas is excellent. Because of the frequency of this tumor in the population, accepted treatments will have wide applications, and those with unsubstantiated efficacy, including the radiation from ablation, are likely to do much more harm than good.
Therapies for the uncommon variants of papillary carcinoma, such as tall cell or insular, have not been thoroughly studied, but it is difficult to see how ablation would be helpful for patients with these neoplasms. Follicular carcinomas have recently been classified as minimally invasive (capsule only), moderately invasive (angioinvasion), and widely invasive (11), distinctions that appear to be helpful in addition to the prognostic schemes of MACIS (metastases, age, completeness of resection, invasion, size) and TNM (12).
Recently, an editorial created by many contributors discussed and promoted recombinant human thyroid-stimulating hormone for ablation (13). Recombinant thyroid-stimulating hormone has not been approved by the Food and Drug Administration for treatment with 131I. In the past, 131I ablations and 131I treatments of thyroid carcinoma have sometimes been used interchangeably, but the differences must now be addressed. Except when a large amount of residual thyroid tissue inhibits TSH secretion after an incomplete surgical thyroidectomy, ablation has no role. Thyroidectomies should be performed by well-trained surgeons; incomplete thyroidectomies should then be uncommon. We believe that research should focus on how better to treat health-impairing and life-threatening carcinomas for which 131I is an important therapy.
FOOTNOTES
COPYRIGHT © 2009 by the Society of Nuclear Medicine, Inc.
References
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