Patients with thyroid cancer and type 2 DM were identified through admission data from Chang Gung Memorial Hospital (CGMH) in Linkou, Taiwan between January 2001 and December 2010. All subjects were Chinese residents of Taiwan. Permission was obtained from the Institutional Review Board (IRB) and ethics committees of CGMH for a retrospective review of the medical records of study subjects. The IRB waived the requirement for obtaining informed consent. Confidentiality of the research subjects was maintained in accordance with the requirements of the IRB of CGMH.
20 years of age and were included in this study if the indication for hospital admission was a diagnosis of thyroid cancer (code 193) and DM (code 250) in the International Classification of Disease-9 (ICD-9) clinical modification format. Type 2 DM was defined as a fasting glucose level >126 mg/dL, or a postprandial glucose level >200 mg/dL or a history of type 2 DM under treatment 
. The clinical data was extracted as previously described 
from the thyroid cancer database of the thyroid cancer team at the cancer center of CGMH that was established in 1994.
During the study period, 1,687 patients with well-differentiated thyroid cancers with different histological patterns were enrolled. Of these patients, 122 also had type 2 DM. All thyroid carcinomas were pathologically classified according to World Health Organization (WHO) criteria 
. All patients were staged by International Union against Cancer-tumor-node-metastasis (UICC-TNM) criteria (6th
. Clinical postoperative progression was defined as lesions confirmed by cytology, pathology, or detectable stimulated thyroglobulin (Tg) levels (>1.2 ng/mL) for well-differentiated thyroid cancer of follicular cell origin and basal calcitonin levels above normal values (>20 pg/mL) for medullary thyroid carcinoma with any evidence suggesting a malignant lesion in imaging studies. Recurrence of thyroid cancer was defined as thyroid cancer present 1 year after thyroid surgery with or without remnant ablation with radioactive iodine (131
I) for thyroid cancers of follicular cell origin.
Of the 122 type 2 DM patients, 18 underwent diet control only. In addition to diet control, 101 patients received oral hypoglycemic agent (OHA) treatment, and 3 received insulin therapy only. Of the 101 patients who underwent OHA treatment, 9 patients also had insulin therapy. The most commonly used OHA was metformin (72 out of 101 cases) either alone or with different sulfonylurea drugs. Other patients (29 cases) received α–glucosidase inhibitors, thiazolidinediones, or dipeptidyl peptidase IV inhibitors.
For papillary and follicular thyroid carcinomas, thyroid remnant ablation was performed 4 to 6 weeks after surgery. The 131I ablation dose for most patients was 1.1 GBq (30 mCi). A whole body scan (WBS) was performed 1 week after 131I administration using a dual-head gamma camera (Dual Genesys, ADAC, USA) equipped with high-energy collimator. A whole body image was acquired by continuous mode scanning at a speed of 5 cm/min. L-Thyroxin treatment was then initiated to reduce thyroid stimulating hormone (TSH) levels without inducing clinical thyrotoxicosis. Cases in which the foci of 131I uptake extended beyond the thyroid bed were classified as persistent disease or metastases. Such patients were given increased therapeutic doses at 3.7–7.4 GBq (100 to 200 mCi); hospital isolation was arranged at doses exceeding 1.1 GBq, and a WBS was performed 2 weeks after administering the higher therapeutic dose of 131I. Serum Tg levels were measured using an IRMA kit (CIS Bio International, Gif Sur Yvette, France).
Admission records were surveyed for the following data: age, gender, BMI, primary tumor size, ultrasonographic findings, fine needle aspiration cytology results, thyroid function before surgery, surgical methods, histopathologic findings, TNM staging, 1-month postoperative serum Tg levels for thyroid cancer of follicular origin and calcitonin for medullary thyroid cancer, Tg antibody, diagnostic results and therapeutic 131I scanning, 131I accumulated dose, postoperative chest X-ray findings, clinical status for analysis of distant metastases via noninvasive radiological and nuclear medical study examination, treatment outcomes, causes of death, diagnosis of secondary primary cancer, and survival status. In addition, chart records were reviewed for type 2 DM patients. Data concerning DM duration, therapeutic methods, and hemoglobin A1c (HbA1c) levels were analyzed.
All data are expressed as mean ± standard error of the mean. Univariate and multivariate statistical analyses were performed to determine the significance of various factors using the Kaplan-Meier method and logistic regression 
. Statistical significance was indicated by p
<0.05. In addition, survival rates were calculated using the Kaplan-Meier method, and survival rates were compared using Breslow and Mantel-Cox tests.