BOSTON – A study of over 60 years of patient data from the Mayo Clinic suggests a reconsideration of the routine use of unilateral thyroid lobectomy (UL) as the initial treatment for papillary thyroid microcarcinoma.
“Papillary thyroid microcarcinoma [PTM] patients have a normal life expectancy and typically are cured by adequate tumor resection. More than 99% of PTM patients are not at risk of either distant spread or mortality from cancer,” said Dr. Ian D. Hay of the Mayo Clinic, Rochester, Minn. Unilateral thyroid lobectomy is one treatment option for papillary thyroid microcarcinoma along with conventional bilateral nodal resection approaches of near-total thyroidectomy (NT) or total thyroidectomy (TT), or selective radioactive iodine remnant ablation (RRA).
Awareness of PTM is not new; examination of thyroid glands at autopsy going back decades has revealed their presence in 6%-36% of samples. A more recent development is the use of high-resolution ultrasound-guided biopsies of papillary thyroid carcinoma (PTC) lesions as small as 3 cm. For example, at the Mayo Clinic the diagnosis of PTM was about one annually from 1935 to 1944, while from 2005 to 2014 the average was close to one per day. “At Mayo, 34% of PTCs seen since 1995 are PTMs,” Dr. Hay said at the annual meeting of the Endocrine Society.
The best initial management of PTMs is disputed, with observation favored by some, TT and RRA favored by others, and ethanol ablation having been found to be effective by institutions including the Mayo Clinic. UL has been deemphasized, despite the 2015 American Thyroid Association Guidelines recommendation of UL as the usual surgical procedure for adults with PTM.
Dr. Hay and his colleagues sought to provide some clarity to the issue by taking advantage of the institute’s database of adult (18+ years) PTM patients who were consecutively treated from 1935 to 2014. The decades of data allowed a long-term look at patient outcomes. They examined data from 1,345 patients, 954 women and 391 men with a median age at surgery of 48 years. The mean follow-up was 15.4 years, representing almost 21,000 patient years. Data on tumor recurrence and cause-specific mortality were derived from a data base of over 4,300 PTC patients representing over 66,000 patient-years of observation.
Median tumor size was 7 mm (range, 0.08-1.0 cm). Extrathyroid invasion was evident in 18 (1.3%) cases and 298 tumors (26%) were multifocal. There were 399 (30%) node-positive tumors at diagnosis and 4 (0.3%) cases featuring initial distant metastases.
The mean MACIS (metastasis, age at presentation, completeness of surgical resection, invasion [extrathyroidal], size) score was 4.25 with little variation in score over time. Almost all (96%) patients had a MACIS score of under 6. Bilateral lobar resection was done in 1,132 (95%) patients, with NT or TT comprising 80% of the cases. UL was done in only 202 (15%) cases. The use of TT skyrocketed from 3% of the cases done in the first 2 decades to 40% in the last 2 decades. Regional nodes were removed at surgery in 743 (55%) cases, either by “node picking” (23%) or compartmental dissection (32%).
Overall survival following surgery in PTM patients was similar to age- and gender-matched controls (397 deaths observed, 431 deaths expected; P = .16). Only four (0.3%) patients died of PTM. The rates of locoregional recurrence were similar for the unilateral and bilateral approaches (P = .90). In 1,148 patients with potentially curable PTM, defined as the absence of metastasis at diagnosis and no gross residual disease, the rates of tumor recurrence 10, 20, and 40 years after surgery were 6%, 7%, and 10%, respectively. In these 1,148 patients, the 30-year locoregional recurrence rates after UL alone were similar to those seen after NT or TT followed by RRA (P = .99).
UL did not result in permanent unilateral vocal cord paresis or permanent hypoparathyroidism. These adversities were more likely to develop following bilateral lobectomy.
“Since [UL] produces comparable recurrence results when compared to bilateral surgery and is not associated with either cord paresis or hypoparathyroidism, then perhaps it is overdue for institutions like Mayo to individualize our treatment policies and more often employ UL when surgery, and not observation or ultrasound-guided percutaneous ethanol ablation, is chosen to treat PTM,” said Dr. Hay.
Dr. Hay was adamant on the overuse of ultrasound in the detection of small-diameter carcinomas in the decision for bilateral surgery. “It’s embarrassing how much we are wasting resources and doing too much ultrasound too often,” he said in an interview.
Dr. Hay had no disclosures.