Coexistence of thyroid autoimmunity and thyroid cancer

Coexistence of thyroid cancer and autoimmune thyroid disorders (AITD) may arise due to the frequent occurrence of autoimmunity. The coincidence of differentiated thyroid cancer (DTC) with Hashimoto's Thyroiditis (HT) has been variably reported at between 0.5 and 22.5%. Thyroid peroxidase antibody (TPOAb) measurement is useful in diagnosing patients with AITD, and anti-thyroglobulin autoantibody (TgAb) is used to detect potential interferences with thyroglobulin (Tg) immunoassays. Tg is used as an exquisite tumour marker in DTC patients. Our study aimed at finding out the coexistence of thyroid autoimmunity in known cases of thyroid cancer patients, those approaching our OPD for follow-up; using TgAb and TPOAb measurement. The study comprised male (n=30) and female (n=62) DTC subjects in the age group of 18-70 yrs. Upper reference ranges for TgAb and TPOAb were established at 30 and 12 IU/ml respectively in our laboratory, using commercial isotopic kits from Immunotech, France. In the total study subjects, the occurrence of TgAb and TPOAb were 17.3% (16/92) and 15.2% (14/92) respectively, and 26% (M/F ratio, 0.33) were positive for TPOAb and/or TgAb. Of the TgAb-positive subjects, 37.5% (6/16) were also TPOAb-positive, and of the TPOAb-positive subjects, 42.85% (6/14) were also TgAb-positive with M/F ratio of 0.2. In conclusion, significant co-occurrence of TgAb and/or TPOAb in thyroid cancer implies that autoimmunity does coexist with thyroid cancer and therefore, for better clinical management these patients (especially women) should have a careful follow-up. Nonetheless, few studies have reported that the presence of thyroid autoimmunity may indicate a better prognosis for thyroid carcinoma. Another consequence of this coexistence is methodological, pertaining to the use of Tg as a tumour marker in the presence of TgAb, thereby restricting its application in such patients. Subsequently, in such cases, for better management of DTC patients, TgAb concentrations measured by the same method may act as 'surrogate' tumour marker. (author)