Endocrine Abstracts

The treatment of papillary thyroid cancer consist of surgery and if indicated post-surgical administration of radioiodine with the initiation of thyroid hormone substitution. Whether or not a patient receives a post-operative radioiodine treatment largely depends on the pathological staging (TNM).

Through observational data, the benefit of additional radioiodine treatment was only significant in patients with thyroid cancer classified as high risk according to the characteristics described by the American thyroid association (pT4, proven metastatic disease). In ATA low risk patients (T1a) post-operative radioiodine treatment is not suggested as there is no evidence suggesting the iodine treatment effects the long term outcome. In ATA low risk patients (T1b, T2) and ATA intermediate risk patients (T3 – tumor size>4 cm) radioiodine therapy may be considered if other adverse characteristics are present, for example an aggressive histology. In ATA intermediate risk patients (T3 with microscopic extrathyroidal extension, T1–3 N1a, T1–3 N1b) radioiodine treatment is generally favoured due to the higher risk of persistent or recurrent disease.

Case 1: A 33-year old female patient diagnosed with a follicular variant of papillary thyroid cancer underwent a total thyroidectomy in 2017. The postoperative staging consisted of a pT1b lesion of 2.4 cm limited to the thyroid gland for which postsurgical iodine treatment is not routinely recommended. Through multidisciplinary consultation, it was decided to treat the patient with 30 mCi radioiodine as the thyroglobulin was 0.75 ng/ml four months post-operative. The post therapy total body 131I scintigraphy with SPECT-CT showed several foci of costovertebral and pelvine iodine uptake without CT-graphic nor MRI correlates. It was decided to conceive these hotspots as micro-metastases, indicating the need of an additional treatment with 100 mCi radioiodine. Post therapy there were no clinical, biochemical (undetectable thyroglobulin) and scintigrafic residual tumor foci.

Case 2: A 37-year old female patient was diagnosed with a follicular variant of papillary thyroid cancer after a right robot-assisted hemithyroidectomy. The patient underwent a completion thyroidectomy in 2019. Pathological examination showed a lesion of 7 cm limited to the thyroid gland, indicating a pT3 staging. For this type of lesion the American thyroid association guidelines indicate to consider additional radio-iodine therapy if other adverse features are present. In this case there were none. Nevertheless the decision was made to give the patient an adjuvant treatment with 100 mCi radioiodine since the thyroglobulin level two months post-operative was 0.80 ng/ml. Post therapy scan showed two foci of pelvine iodine uptakes. CT showed no corresponding lesions. MRI showed a small focus of sclerosis left supra-acetabular with minimal surrounding bone oedema (17 mm). A targeted biopsy was not possible, but morphologically the lesion was highly compatible with a bone metastasis. Six months after radioiodine therapy thyroglobulin is undetectable. Morphologic follow up is planned.

By following the guidelines based on the pathological staging, both patients do not have a formal indication for radioiodine treatment. These cases illustrate the importance of including the post-operative thyroglobulin level in the decision-making process whether or not to administer post-surgical radioiodine treatment. The nadir of postoperative serum thyroglobulin level is usually reached 4 weeks postoperatively. Observational data have shown that a thyroglobulin level around 0.2 ng/ml has the best sensitivity and specificity for detecting persistent disease. In conclusion: combining TNM staging and post-operative thyroglobulin allows for selective radioiodine use as well as for detection of unexpected metastatic disease.

References: 1. Schlumberger M. Pacini F. Tuttle R. M. Thyroid tumors. 4th edition. Montreuil-sous-Bois: TC Graphite, 2015. Chapter 7:Initial treatment; p. 141–169.

2. Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2016;26(1):1–133. doi:10.1089/thy.2015.0020