Outcome of thyroid ultrasound screening in FAP patients with a normal baseline exam

Familial adenomatous polyposis (FAP) is a hereditary cancer syndrome associated with a substantial lifetime risk for colorectal cancer. The leading extra-colonic causes of cancer in FAP include duodenal and thyroid cancer (TC). Recent guidelines recommend annual thyroid ultrasound (TUS) screening beginning in the teenage years but the evidence to support the interval particularly in FAP patients with a normal baseline ultrasound is lacking. TUS results from FAP patients enrolled in a thyroid screening program from 2006 to 2016 and who had at least 2 TUS were reviewed. TUS findings were classified as normal, low (LR) or high risk (HR) for TC based on nodule characteristics as determined by American Thyroid Association (ATA) guidelines. We assessed the incidence of TC in patient with normal baseline TUS and factors associated with TC. 264 FAP patients were included. Baseline TUS was normal in 167, LR in 74, and HR in 24 patients. Patients were observed for a mean 4.8 years and underwent an average of 3 TUS. Patients with normal baseline TUS did not develop TC during the course of follow up of 5.1 years. TC developed in 6 patients (2.3%) all with baseline nodules; 5 in the LR group and 1 in the HR group. Factors associated with development of TC were presence of baseline nodule(s) and female sex. The development of TC in FAP patients in a TUS screening program with short term follow up is low and no FAP patient with a normal baseline TUS developed TC during observation. Annual TUS in patients with a normal baseline TUS may not be needed. Extending the screening interval to 2 years may be reasonable until nodules are detected.