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Radioactive Iodine Does Not Provide Additional Benefit to Surgery for Papillary Thyroid Microcarcinoma: Presented at ECE

By Chris Berrie

BERLIN -- May 7, 2008 -- More than 99% of patients with papillary thyroid microcarcinoma (PTM) are not at risk of either distant spread or mortality from cancer after total thyroidectomy and these patients do not benefit from additional radioiodine ablation, according to analysis of data from the KIMS Pfizer international metabolic database.

This long-term follow-up study was presented here on May 5th at the 10th European Congress of Endocrinology (ECE), by principal investigator Ian Hay, MD, PhD, Professor of Medicine, Division of Endocrinology, Mayo Clinic, Rochester, Minnesota.

A PTM is classified as being 1 cm or less in diameter, according to the World Health Organisation, and they have long been known to be present in 6% to 36% of thyroid glands after meticulous autopsy examination.

However, controversy remains around the therapeutic options of patients with PTM, especially as they are increasingly being recognised through the more widespread use of high-resolution ultrasound.

"The unique aspect of this study is that these patients have been studied over a period of 60 years during a time of increasing intensity of surveillance and aggression of therapy," Dr. Hay said.

The study's aim was to describe the postsurgical outcomes in 900 consecutive patients with PTM treated at the Mayo Clinic from 1945 to 2004, in order to develop an "appropriately aggressive" management programme for these patients, he said.

Prognosis was determined using 3 common methods: (1) AMES, which takes into account the age of the patient, presence of distant metastases, extent of the primary tumour, and the size of the primary cancer; (2) AGES score, which is derived from the age of the patient, histological grade of the tumour, extent of tumour invasion, and size of the primary tumour; and (3) MACIS, a prognostic scheme that uses metastasis, patient age, completeness of resection, local invasion, and tumour size.

Mean age at diagnosis of PTM was 46 years; mean follow-up of these patients was 17.2 years. At the last follow-up visit, 3 deaths (0.3%) were attributed to PTM, 1 patient (0.1%) was living with lung metastases, 633 patients (70.3%) were free of PTM, and 263 patients (29.2%) had died of other causes.

The all-cause mortality rate was not significantly different from what was expected for the control Minnesota population (265.2 subjects). And no significant differences were found between observed and expected survival rates based on the US decennial life tables for the period between 1970 and 2000 (P = .96), Dr. Hay said.

Surgical pathology findings indicated a mean tumour size of 7 mm (range, 1-10 mm), with 98% of patients having histological Broders grade 1. At diagnosis, multiple tumour foci were found in 23% of patients (12% bilateral); 30% were node positive, and 0.3% had distant metastases. Overall, 99% were AMES low-risk, 98% had AGES score <4, and 96% had MACIS prognostic score of <6.

Locoregional recurrence rates (LRRs) were not significantly different in the 125 patients who underwent unilateral lobectomy and 758 who had bilateral lobar resection throughout the analysis period (P = .540). These were not significantly lower after total thyroidectomy than after near-total or bilateral subtotal surgery.

Radioiodine remnant ablation (RRA) did not have a significant impact on tumour recurrence at local or distant sites, Dr. Hay said. And although neck nodal metastases were found more frequently in patients who underwent RRA, this may be because patients who are node positive are 10 times more likely to receive RRA, he explained.

Finally, for the subset of patients that received RRA treatment who were analysed according to tumour foci and nodal status, RRA did not significantly improve outcomes in any situation, Dr. Hay said.

"I think that the key here is that adequate surgery is curative and radioactive iodine does not aid an excellent prognosis in this particular group of patients," Dr. Hay concluded.


[Presentation title: Neither Total Thyroidectomy Nor Radioiodine Remnant Ablation Improved Long-Term Outcome in 900 Patients With Papillary Thyroid Microcarcinoma Treated During 1945 Through 2004. Abstract P404]

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