An Investigation of the Risk Factors of Differentiated Thyroid Cancer by Meta-Analysis

Abstract

INTRODUCTION: Thyroid cancer is the most common endocrine malignancy and its incidence is increasing, of which the most common subtype is papillary thyroid cancer. Risk factors for papillary thyroid cancer have been investigated extensively. Given the good prognosis of papillary thyroid cancer there is growing concern regarding the development of second primary malignancies following thyroid cancer. This study specifically considered breast cancer is the most common cancer in women and has been theorized to be associated with thyroid cancer under certain conditions. Multifocality is a risk factor for thyroid cancer that has not been extensively studied. Age is seen as a significant prognostic feature for all cancers. There has been few studies considering the effect of thyroidectomy for thyroid cancer in the elderly. This thesis aimed to add to the body of literature on risk factors for thyroid cancer to provide some insight and suggestions into the investigation, management and screening of the disease. METHOD: A series of three meta-analyses were performed to investigate risk factors of thyroid cancer and to determine its prognostic significance. We followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. A systematic search of the databases MEDLINE (from 1950), PubMed (from 1946), to identify relevant articles. Relevant data was tabulated then analyzed using Comprehensive Meta-Analysis software to determine summary effect. RESULTS: This study identified an association between breast cancer and thyroid cancer. It found that there is a greater risk of thyroid cancer following breast cancer than breast cancer following thyroid cancer. Additionally, multifocality was confirmed as a significant risk factor for disease progression, showing increased risks of lymph node metastases, extrathyroidal extension and recurrence. Finally, this thesis emphasized the increased risk of thyroidectomy for thyroid cancer in the elderly, demonstrating that risk of mortality, recurrence and post-operative complications is increased in patients above the age of 60. CONCLUSIONS: Finding as association between breast cancer and thyroid cancer opens up new opportunities for research into the association between the two cancers. Increased risk can direct clinicians to guide investigations and screening. Multifocality as a risk factor for thyroid cancer can guide clinical decision making regarding operative and post-operative management. The increased risk of mortality, recurrence and complication rates in elderly patients suggest that patients should undergo aggressive surgical management as early as possible to reduce risk of mortality and morbidity for the patient. The current thesis provided evidence that the above mentioned risk factors should influence investigation, management and screening for patients diagnosed with thyroid cancer.