Differentiated Thyroid Ca -- Diagnostic Imaging and Radionuclide Therapy Revised American Thyroid Association Management Guidelines 2009. Part 2: Initial Management of Differentiated Thyroid Cancer

Histologic variants (tall cell, columnar cell, diffuse sclerosing) of papillary thyroid cancer (PTC) have a worse prognosis, as do more invasive variants of follicular type. Intermediate risk of recurrence includes (1) microscopic invasion of tumor into the perithyroidal soft tissues, (2) cervical lymph node metastases, (3) I-131 uptake outside the thyroid bed, (4) aggressive histology, or (5) intrathyroidal vascular invasion. High-risk of recurrence includes (1) gross tumor invasion, (2) incomplete tumor resection, (3) distant metastases, and possibly (4) elevated thyroglobulin unexplained by uptake on posttreatment I-131 scan. Postoperative I-131 remnant ablation facilitates the early detection of recurrence based on serum Tg measurement and/or I-131; in addition, the post-therapy scan identifies previously undiagnosed disease, especially in the lateral neck. Furthermore, this first dose of I-131 eliminates any thyroid cancer cells remaining after surgery in patients at risk for recurrence or disease-specific mortality. I-131 ablation is recommended for all patients with distant metastases, gross extrathyroidal extension, or primary tumor size >4 cm. For 1to 4-cm thyroid cancers confined to the thyroid with lymph node metastases or other higher-risk features, I-131 ablation is not recommended for primary tumors <1 cm, even if multifocal. Children achieve the adequate TSH elevation by 2 weeks of Synthroid withdrawal. For patients being prepared for ablation by hormone withdrawal, T4 may be resumed on the second or third day after I-131 therapy. Thyrogen was approved for preparation of ablation in December 2007, and this approach is "strongly recommended" by the new the American Thyroid Association (ATA) guidelines. What activity of I-131 should be used for remnant ablation? A recent prospective, randomized study found no significant difference in the remnant ablation rate using 30 or 100 mCi of I-131. However, if residual microscopic disease is suspected, or if there is a more aggressive tumor histology (eg, tall cell, insular, columnar cell carcinoma), then higher activities (100 to 200 mCi) are appropriate. Low-iodine diets (<50 μg/day) increase the effective radiation dose. A low-iodine diet for 1 to 2 weeks is recommended for patients undergoing I-131 remnant ablation. Post-therapy whole-body iodine scanning conducted approximately 1 week after I-131 therapy visualizes additional metastatic foci in 10% to 26% of patients compared with the diagnostic scan. Look for new abnormal uptake in the neck, lungs, and mediastinum. Reviewer's Comments: New developments are being reported, particularly in the detection of molecular and genetic markers, which the guidelines acknowledge without a specific recommendation. While the published guidelines provide education as well as clinical advice, the best advice is to keep current. I wonder whether the ATA will have to publish another sooner-than-expected update to its guidelines in the next couple of years. The current guidelines are printed in the November 2009 issue of Thyroid. (Reviewer-).