Abstract
We are very pleased to learn of the interest Drs. Rosário and Côrtes (1) have shown in our recent article published in Thyroid (2). The subject of the article requires additional study and thus remains an area for discussion. Our study documents the experience of multiple high-volume institutions using multiple thyroglobulin antibody (TgAb) assays and thus represents a real-world multi-institutional United States experience. In fact, Drs. Rosário and Côrtes acknowledge in their article the limitations associated with utilizing a single TgAb assay (3). Since multiple TgAb assays were utilized and also potentially changed over time, the TgAb assessment in our study is qualitative. We are pleased that Drs. Rosário and Côrtes noted a de novo TgAb prevalence rate similar to ours, in their prospective single-institutional study.
As one would anticipate, our subjects' individual TgAb results after obtaining de novo TgAb status ranged from persistently positive to varying degrees of intermittent positivity to reversion to negative status (with a varying number of additional follow-up measurements). We did not detect an obvious difference in the clinical significance among these de novo TgAb subgroups, but the limited number of patients in each subgroup does not allow for any definitive conclusions to be drawn. In the recent article by Reverter et al., referenced by Drs. Rosário and Côrtes, 2 of 16 (12.5%) patients with de novo TgAbs above the assay's functional cutoff level were diagnosed with a structural incomplete response (4), a rate very similar to our 6 of 40 (15.5%) (2). Structural recurrence in the persistently TgAb negative group is not specifically mentioned by the authors.
The recent abstract presented by Fatemi et al., also cited by Drs. Rosário and Côrtes, differed significantly from our study (5). This study relied on historical controls and furthermore included patients who were initially TgAb positive, became seronegative, and then reverted to positive (38% of their population). Furthermore, in their article, Drs. Rosário and Côrtes acknowledge the limitation of not having directly compared subjects with borderline TgAbs with those with elevated TgAbs (3).
We appreciate the comments offered by Drs. Rosário and Côrtes and we have recognized the limitations of our study. Nevertheless, we stand by our stated conclusion that larger prospective studies are required to confirm these findings and further assess the significance of de novo TgAb development in the follow-up of patients with differentiated thyroid cancer (2).