PARIS – An ultrasensitive chemoluminescent thyroglobulin assay can identify which differentiated thyroid cancer patients may require more intense follow-up after surgery, as well as those with a low risk of persistent or recurrent disease.
“In patients with a low basal thyroglobulin (less than 0.15 ng/mL), follow-up can be simplified, while in patients with a higher basal level, periodic examination and regulation are probably required,” Dr. Pasqualino Malandrino said at the International Thyroid Congress.
Dr. Malandrino of the Garibaldi-Nesima Hospital in Catania, Italy, and his colleagues employed the ultrasensitive assay in 425 consecutive patients who had been treated for differentiated thyroid cancer in 2006-2010. All had undergone a total thyroidectomy followed by radioiodine ablation. No patient had any evidence of residual disease, and all had a basal thyroglobulin level of less than 1 ng/mL.
Of the cohort, 337 were women; their mean age at diagnosis was 44 years. There were 406 papillary and 19 follicular cancers among them. All patients were negative for antithyroid antibodies and all were receiving recombinant TSH as scheduled.
All of the patients had their thyroglobulin measured with the ultrasensitive chemoluminescent assay before and after receiving recombinant TSH. The investigators defined persistent disease as a stimulated thyroglobulin value exceeding 2 ng/mL.
Most of the patients (331) had a baseline thyroglobulin level of less than 0.10 ng/mL and a median TSH level of 0.21 microIU/mL. The thyroglobulin level was 0.11-0.50 ng/mL in 80 patients, with a median TSH of 0.15 microIU/mL; 14 had a thyroglobulin level of 0.50-1 ng/mL with a median TSH of 0.19 microIU/mL.
After the patients underwent TSH stimulation, the ultrasensitive assay determined that thyroglobulin levels were 2 ng/mL or higher in 1% of those in the lowest tertile of basal thyroglobulin levels, in 29% of those in middle tertile, and in 71% of those in the highest tertile.
A basal thyroglobulin cutoff value of 0.15 ng/mL was the most accurate predictor of residual disease. Using this cutoff, a stimulated thyroglobulin of 2 ng/mL or greater was found in 1% of those with a basal thyroglobulin of 0.15 ng/mL or less, compared with 45% of those with a baseline level of more than 0.15 ng/mL.
The marker had a sensitivity of 87% and a specificity of 91%, a negative predictive value of 99% and a positive predictive value of 48%.
However, Dr. Malandrino added, “the low positive predictive value of the 0.15 ng/mL cutoff means that we require additional investigation to be able to identify very-high-risk patients.”
Dr. Malandrino did not disclose any financial conflicts.