Is T1a and T1b Staging Necessary in Differentiated Thyroid Cancer?

Senior Author Julie A. Sosa, MD and Robert C. Smallridge, MD comment

While patients with pT1a and pT1b differentiated thyroid cancer underwent different treatment strategies during the last decade, survival outcomes were similar, according to a retrospective analysis in the August issue of Thyroid. The findings, along with the recent changes in the American Thyroid Association treatment guidelines for thyroid cancer, may make tiered T1 staging unnecessary in this population, the study authors found.
Woman having an ultrasound test performed on the thyroid“Based on the 2015 American Thyroid Association (ATA) and National Comprehensive Cancer Network (NCCN) guidelines,  either lobectomy or total thyroidectomy can be performed for low-risk tumors, and radioactive iodine administration is not really indicated; given these guidelines, it might be anticipated that treatment differences will diminish going forward,” explained senior author Julie A. Sosa, MD.

“Therefore, division of the AJCC [American Joint Commission on Cancer] staging system for T1 tumors into T1a vs T1b subgroups may become obsolete over time,” said Dr. Sosa, who is Professor of Surgery and Medicine, Chief of the Section of Endocrine Surgery, Director of the Surgical Center for Outcomes Research (SCORES), and Leader of the Endocrine Neoplasia Diseases Group at Duke Cancer Institute and Duke Clinical Research Institute in Durham, NC.

This study confirms other recent findings showing similar survival outcomes for T1a and T1b thyroid tumors, but in a larger population, commented Robert C. Smallridge, MD, Deputy Director of the Mayo Clinic Cancer Center, Alfred D. and Audrey M. Petersen Professor of Cancer Research, Professor of Medicine at Mayo Clinic in Jacksonville, Florida, and Past President of the American Thyroid Association.

“Up until recently, lobectomy was used to manage tumors <1cm, often found incidentally, and thyroidectomy was used for tumors ≥1 cm,” Dr. Smallridge said. “However, total thyroidectomy increases the risk of complications even in excellent surgeons’ hands. Thus, many surgeons are moving toward offering similar types of treatment for 1-2 cm thyroid tumors as we use for microcarcinomas. In addition, the recent ATA guidelines increased the size for which lobectomy should be considered as an option for tumors up to 2 cm.”

Large Retrospective Study
The researchers examined data from all adult patients with pathologic tumor size <1 cm (pT1a; n=98,111) or 1-2 cm (pT1b; n=51,801) differentiated thyroid cancer in the National Cancer Data Base (NCDB; 1998–2012). The Surveillance, Epidemiology, and End Results (SEER) program (2004–2012) was used to determine disease-specific survival for patients with pT1a (n=11,208) or T1b (n=7,173) disease.

“This study is one of the largest studies on low-risk DTC [differentiated thyroid cancer], and the first to evaluate survival and treatment strategies under the current American Joint Committee on Cancer (AJCC) staging system in a national analysis,” Dr. Sosa noted.

Difference in Management Found
“We found that differences in management exist between pT1a (<1 cm) and pT1b (1-2 cm) tumors,” Dr. Sosa said, explaining that pT1b tumors are 57% more likely to undergo total thyroidectomy and 72% more likely to receive RAI [radioactive iodine] postoperatively than pT1a tumors. “However, after we adjusted for treatment differences, both overall and disease-specific survival for patients with pT1a and pT1b DTCs were similar (P=0.23 and 0.93, respectively).”
Table. Clinical and Pathological Differences in Patients With  pT1a and pT1b TumorsDr. Sosa said the similarity in survival is not unexpected, “since several studies have shown that low risk tumors that are small, intrathyroidal, and without lymph node or distant metastases, generally have excellent outcomes overall. Given this, it appears that the division of T1a vs T1b in the current AJCC staging system may not be really necessary.”

“I think everyone would agree that survival is excellent regardless of T1 status,” Dr. Smallridge said. That finding was not surprising, he noted.

“Interestingly, there were a number of differences between the two groups that might affect recurrence rate,” Dr. Smallridge said. “For example histology was significantly different in terms of the number of follicular and Hürthle cell tumors among patients with T1a and T1b tumors. While these were not large numbers, they were still 3 to 4 times as many cases in the T1b group. In addition, there was more lymphovascular invasion, positive margin status, and positive lymph nodes in the T1b group. Those are all factors that empirically might increase the risk for recurrence, but we simply don’t have that data in this study.

“Other studies that have followed these rates suggest that the frequency of recurrence appears to be about the same for T1a and T1b tumors. In addition, only a small percentage of patients would be expected to experience recurrence,” Dr. Smallridge said.

“Another study limitation is that it is unclear how long patients were followed in this study,” Dr. Smallridge said. “While the survival curve shows a long duration, the study does not report how many patients were followed in those later years.”

Treatment Decisions in Differentiated Thyroid Cancer Should Be Individualized
“Tumor size alone likely does not represent the only, or even the best, way to evaluate papillary thyroid cancer risk,” Dr. Sosa said. “A thorough preoperative radiologic evaluation of the neck to seek out possible clinical metastatic disease to the lymph nodes, or evidence of extrathyroidal extension should be undertaken for all patients, regardless of the size of the primary tumor.”

“The risk of surgery and the risk of morbidity and mortality from the cancer should be weighed for each patient, so that the best treatment plan may be put in place,” Dr. Sosa said. “This requires a team approach between an experienced endocrinologist, radiologist, thyroid surgeon, pathologist, and the patient. The risks of surgery, complications, adjuvant treatment, and expected outcomes should be discussed. The patient also should understand that thyroid cancer staging is frequently a dynamic process, given the fact that patients have excellent survival, but surveillance for potential thyroid cancer recurrence should extend beyond the treatment phase.”

Dr. Smallridge said that it may be best to determine T1a staging because several other treatment options are under investigation and may require distinguishing between T1a and T1b tumors. The primary option being studied is active surveillance, Dr. Smallridge noted. He pointed to the long-term trial by Miyauchi et al showing that both immediate surgery and active observation of microcarcinomas showed excellent outcomes. Ultrasound-guided percutaneous ethanol ablation also is being investigated as an alternative to surgery.

“I expect that in the next 5 to 10 years, we are going to study these other options in T1a and T1b populations separately,” Dr. Smallridge concluded.

August 24, 2016

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