Endocrine Abstracts

Background: Assessment of response to therapy is a valid tool for dynamic risk stratification in patients with differentiated thyroid cancer (DTC). It is well documented in patients treated with total thyroidectomy and radioiodine ablation therapy (RAI), but data is still sparse regarding patients treated with lobectomy. Our study aimed to evaluate response to therapy in patients with DTC treated with lobectomy.

Methods: We performed a retrospective study of 69 patients identified from our institutional database, who underwent lobectomy for DTC between 2000 and 2015. All patients had apparent complete tumour resection, without clinically apparent lymph node or distant metastasis at diagnosis and nonaggressive histologic variant. Excellent response to therapy was defined as stable, nonstimulated thyroglobulin (Tg) <30 ng/ml and negative imaging and indeterminate response was defined by nonspecific findings on imaging studies or rising Tg levels. Statistical analysis was performed using SPSS v23.0.

Results: All patients were followed for a minimum of 3 years post-operatively (79.5±44.3 months). Forty patients (57.9%) had microcarcinomas and mean tumour size was 11.7±11.5 mm. Twenty patients (28.9%) had completion thyroidectomy and RAI in the first year after lobectomy due to the presence of contralateral nodules or extra-thyroidal extension, and half of these had malignant disease. These patients had a similar level of post-surgery (Tg) (22.1 ng/ml versus 18.3 ng/ml; P=0.646) to patients who did not undergo completion thyroidectomy. All of these patients had excellent response to therapy. At the end of the follow-up, 51% of the patients who did not undergo completion thyroidectomy, had contralateral nodules and these patients had a higher level of Tg at the end of the follow-up than patients who had no nodules (13.2 ng/ml versus 3.9 ng/ml; P=0.02). Eleven patients (15.9%) had indeterminate response to therapy at the end of the follow-up, based on ultrasound findings or rising Tg levels. These patients had similar levels of post-surgery Tg levels (19.4 ng/ml versus 17.6 ng/ml; P=0.451) to patients with excellent response to therapy but higher Tg levels at the end of the follow-up (13.1 ng/ml versus 6 ng/ml; P=0.03).

Conclusion: Outcomes are excellent in selected patients with DTC treated with lobectomy. Indeterminate response to therapy does not seem to affect overall survival and post-surgery Tg levels do not seem to predict response to therapy. In this study, a threshold lower than 30 ng/ml might be more accurate to define excellent response to therapy or even indeterminate response.