Prevalence and Clinical Risk Factors of Thyroid Cancer in Retrosternal Goiter: A Retrospective Comparative Study with Cervical Multinodular Goiter.

Background: Surgical intervention in asymptomatic retrosternal goiter (RSG) is debated in the absence of suspicious cytology, while performing fine-needle aspiration (FNA) is challenging in thyroids with mediastinal extension. The rate of unexpected thyroid cancers found at the time of thyroidectomy varies widely, while the notion of increased cancer incidence in RSG with respect to cervical goiters is still controversial. Methods: We retrospectively reviewed 411 patients with a preoperative diagnosis of multinodular goiter (MNG) (114 retrosternal, 297 cervical) who underwent thyroidectomy at an academic endocrine surgery referral center between January 2019 and October 2022. Rates of cancer detected on the final pathology examination, overall and not anticipated by preoperative workup, were compared between cervical MNG (cMNG) and RSG. Results: Patients with RSG were older (58.2% vs. 50.6%; p < 0.001) and more likely to be men (34.2% vs. 23%; p = 0.014). Overall, thyroid cancer was found in 49.5% of cMNG specimens and in 35.1% of RSGs (p = 0.02), and cancer > 1 cm was found in 37.4% of cMNG and 17.4% of RSG (p = 0.003). Prevalence of unexpected thyroid cancer was not significantly different between cMNGs (29.8%) and RSGs (28.8%). Unexpected carcinomas > 1 cm impacted 11% of all RSGs. Conclusions: In this study, the prevalence of unexpected thyroid cancer in RSG was similar to cMNG and significant from a clinical standpoint, with 1 in every 10 RSG diagnosed with differentiated cancer > 1 cm. Findings may be partially attributed to the difficulty in performing FNA in the mediastinum. Surgeons should counsel patients preoperatively regarding the risk of unexpected thyroid cancer to set appropriate expectations of outcome.