Characteristics of benign and malignant thyroid disease in familial adenomatous polyposis patients and recommendations for disease surveillance

Background: Familial adenomatous polyposis (FAP) is a hereditary colon cancer syndrome that involves multiple extracolonic organs, including the thyroid. Several studies have estimated the rate of thyroid cancer in FAP to occur at five times the rate of the general population, but no current consensus defines screening for thyroid cancer in this cohort. This study seeks to define the features of benign and malignant thyroid disease in FAP patients, to compare thyroid cancer cases found through screening with those found incidentally, and to propose disease surveillance recommendations. Methods: Prospective screening for early thyroid cancer detection with thyroid ultrasound (US) was performed on FAP patients at the time of annual colonoscopy since November 2008. Clinical and US data were reviewed to characterize the observed thyroid nodules. Nonscreening-detected cases (NSD) were found through review of the colon cancer registry database. Results: Eighteen NSD were found, compared with 15 screening-detected (SD) cases, out of 205 total patients screened (M_age=42 years; 55% female). The mean tumor size was larger in the NSD group than the SD group (p=0.04), and they tended to demonstrate more positive lymph nodes and more complications than the SD group. In the screened cohort, at least one thyroid nodule was detected in 106 (51.7%) patients, with 90% of these seen on initial exam. A total of 40/106 (37.7%) patients required fine-needle aspiration biopsy of a dominant nodule (M_size=14mm), and 28/40 (70%) of these were performed at the first US visit. Suspicious US features were present in 16/40 (40%) patients, including five sub-centimeter nodules. Cytology and/or nodule US was abnormal in 15/205 screened patients, leading to surgery and revealing 14 papillary and one medullary thyroid cancer. Conclusions: Given the age and sex distribution of the screened cohort, this study reveals a higher-than-expected prevalence of both benign and malignant thyroid disease in the FAP population. Additionally, SD cases seemed to consist of smaller-sized cancers that required less radical therapy compared to NSD cases. Since it was found that the initial US in the screening program accounted for the majority of detected nodules (90%) and biopsies (70%), baseline and subsequent thyroid US surveillance is recommended in all FAP patients.