Abstract 3468: Impact of histology on serum thyroglobulin as a biomarker for nonmedullary thyroid cancer recurrence
Authors: Raki Logesh , Ganguly Rehena , Ngeow Joanne 
Published: August 2015

Abstract
Purpose
Thyroid cancer is one of the most common cancer diagnoses amongst cancer survivors given the overall good prognosis. Thyroglobulin (Tg) is a thyroid but not tumor specific marker. Serum Tg levels less or equal to 0.1 ng/ml in patients without Tg autoantibodies (TgAbs) indicate cure following total thyroid ablation. The major limitations of Tg are false low interferences by TgAbs and a lack of established reference ranges for cured patients with thyroid remnants. Additionally, it is unknown if thyroid histology impacts on its utility as a biomarker for disease recurrence. This retrospective study investigates the relationship between the various histological subtypes of non-medullary thyroid cancers and TG levels to determine whether TG levels are an effective predictor of disease recurrence for all subtypes of differentiated thyroid cancers (DTC).
Methods:
We retrospectively examined all patients with DTC seen at the National Cancer Centre Singapore between January 1, 2004 and March 31, 2014. 745 DTC cases were identified and patient records were examined. Diagnosis of DTC and subtype determination was based on histological analysis of thyroid tissues during fine-needle-aspiration-biopsy(FNAB) or from tissue samples during surgery. DTC recurrence was confirmed by histology or by CT/PET scan. Each patient had blood drawn before Iodine-131 treatments and regular follow up surveillance CT/PET scans as well as following biochemical tests: TSH, free thyroxine, thyroglobulin and TGAb. To avoid interference from the presence of thyroglobulin antibody (TGAb), only patients with TGAb levels below 40IU/ML at baseline were included for the analysis. The association of the histological subtypes with failure of TG levels to rise secondary to recurrence was determined by a Fisher's test.
Results:
463 patients met the inclusion criteria above and were available for analysis of TG as a biomarker for DTC recurrence. The histologies included: 61 (13%) follicular thyroid cancer (FTC), 369 (80%) papillary thyroid cancer (PTC) and 33 others (7%). 52 patients with recurrent DTC was identified with either histological or radiological evidence of disease. An elevated serum TG was found in 94% (49/52) of patients with a recurrence of DTC, of which 81% (42/52) were PTC, 12% (6/52) were FTC. FTC was overrepresented in the 3 patients whereby TG was not predictive of recurrence accounting for 2 of the 3 cases (66% vs 33% PTC; P = 0.06).
Conclusions:
Rise in serum TG is predictive for DTC recurrence in the absence of TgAB interference. Our data suggests that FTCs may be overrepresented in the group where serum TG was not predictive of recuurence. A bigger sample size will be needed to determine if the utility of serum TG is affected by histological subtype.
Citation Format: Logesh Raki, Rehena Ganguly, Joanne Ngeow. Impact of histology on serum thyroglobulin as a biomarker for nonmedullary thyroid cancer recurrence. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3468. doi:10.1158/1538-7445.AM2015-3468