Distinguishing classical papillary thyroid microcancers from follicular-variant microcancers

BackgroundPapillary thyroid microcarcinomas (mPTCs), tumors less than or equal to 1 cm, have been considered the same clinical entity as microfollicular-variant papillary thyroid microcarcinomas (mFVPTCs). The purpose of this study was to use population-level data to characterize differences between mFVPTC and mPTC.Materials and methodsWe identified adult patients diagnosed with mFVPTC or mPTC between 1998 and 2010 in the Surveillance, Epidemiology, and End Results database. Binary comparisons were made with the Student t-test and chi-squared test. Multivariate logistic regression was used to further analyze lymph node metastases and multifocality.ResultsOf the 30,926 cases, 8697 (28.1%) were mFVPTC. Multifocal tumors occurred with greater frequency in the mFVPTC group compared with the mPTC group (35.4% versus 31.7%; P < 0.01). Multivariate logistic regression indicated that patients with mFVPTC had a 26% increased risk of multifocality (odds ratio, 1.26; 95% confidence interval, 1.2–1.4; P < 0.01). In contrast, lymph node metastases were nearly twice as common in the mPTC group compared with the mFVPTC group (6.8% versus 3.6%; P < 0.01). Multivariate logistic regression confirmed that patients with mPTC had a 69% increased risk of lymph node metastases compared with patients with mFVPTC (odds ratio, 1.69; 95% confidence interval, 1.4–2.0; P < 0.01).ConclusionsMultifocality is not unique to classical mPTC and occurs more often in mFVPTC. The risk of lymph node metastases is greater for mPTC than mFVPTC. The surgeon should be aware of these features as they may influence the treatment for these microcarcinomas.