For years the standard treatment for differentiated thyroid carcinoma has been subtotal or total thyroidectomy followed by radioiodine ablation. But experts in the surgical management of thyroid cancer have begun to question this one-size-fits-all approach. Similarly, new rules apply to the post-treatment follow-up for a disease whose burden is quite low compared with other solid tumors.
Jatin P. Shah, MD, PhD, from Memorial- Sloan Kettering Cancer Center, and David S. Cooper, MD, chair of the American Thyroid Association (ATA) Thyroid Cancer Guidelines Task Force offered their perspectives on these new rules in surgical management and follow up.
A wide spectrum of disease
A 2009 study out of Canada compared four methods for Tg quantitation and three methods for detection and quantitation of Tg antibodies (Tg-Ab). They found good agreement between methods for quantitation of Tg, though noted that "closer agreement was expected as the assays are all calibrated to the same reference standard (CRM 457)." However, they found for Tg-Ab assays the rate of antibody positivity ranged from 9% to 21% in their group of patients, and there was agreement in only 6% of cases.
They concluded that "all the thyroglobulin assays appear to be suitable for monitoring patients with thyroid cancer, provided the differences in calibration are taken into account... when changing assays. Conversely, the antithyroglobulin assays are virtually useless, since there appears to be very little agreement...and no evidence of assay interference in the measurements of thyroglobulin" (Clin Biochem 42:416-419, 2009).
"Thyroid cancer is not one disease. It is a spectrum made up of a variety of diseases with different behaviors under one label: thyroid cancer," Dr. Shah said.
"People need to understand the disease before taking on the responsibility of treating it. If you don't understand the disease, then you are perpetuating ignorance in treating your patients," added Dr. Shah, who is professor of surgery and E.W. Strong Chair in Head & Neck Oncology as well as chief of the head and neck service at the New York-based institution.
Increased understanding of the biological progression of neoplastic transformation of thyroid follicular cells has shed new light on the natural history of differentiated thyroid cancer, he said.
"We now know that tumor progression from a well-differentiated to less well-differentiated and undifferentiated carcinoma occurs in a predictable fashion. In addition to histology, other independent parameters of prognosis are age, tumor size, extrathyroidal extension, distant metastasis, and completeness of surgical removal.
Based on these prognostic factors, risk classifications of low, intermediate, and high risk have been developed for differentiated thyroid cancer.
The great majority of patients with thyroid cancer are low-risk, and 70% to 85% of them are cured by their initial operation, whether that is lobectomy or total thyroidectomy. For instance, low-risk patients who have a single intrathytoidal nodule, without any extrathyroid extension, in one lobe while the other lobe is normal are cured by a simple lobectomy. They require no other treatment, Dr. Shah said.
Similarly, low-risk patients with bilobar abnormalities will be cured by total thyroidectomy alone. "At Memorial-Sloan Kettering, for our low-risk patients who undergo total thyroidectomy, we measure their thyroglobulin [Tg] six to eight weeks after surgery. If their unstimulated Tg is 1 ng/ml or less, we consider they are cured. They do not need radioactive iodine(Drug information on iodine)," Dr. Shah said.
He added that the entire idea of total or subtotal thyroidectomy in a patient who needs total thyroidectomy by virtue of bilateral disease or abnormalities, is a wrong concept, yet it is still promulgated. "If you are operating for cancer, why do you want to leave remnant thyroid tissue behind?" he said. "It doesn't make sense to me. If the purpose of the surgery is to treat a thyroid cancer, then there are only two operations: extracapsular lobectomy for a single intrathyroidal nodule or, for bilateral disease, extracapsular total thyroidectomy, leaving no thyroid tissue behind. These will cure the majority of patients."
Dr. Shah acknowledged that high-risk patients, such as those with advanced tumors with invasion of the viscera of the central compartment, require aggressive surgery to remove all demonstrable disease and adjuvant treatment with radioactive iodine or radiation therapy. But these patients are few and far between, he said.