Distinguishing classical papillary thyroid microcancers from follicular-variant microcancers

Abstract

Background Papillary thyroid microcarcinomas (mPTC), tumors less than or equal to 1 centimeter, have been considered the same clinical entity as follicular-variant thyroid microcarcinomas (mFVPTC). The purpose of this study was to use population-level data to characterize differences between mFVPTC and mPTC. Materials & Methods We identified adult patients diagnosed with mFVPTC or mPTC between 1998 and 2010 in the Surveillance, Epidemiology, and End Results (SEER) database. Binary comparisons were made with the student’s t-test and chi-squared test. Multivariate logistic regression was used to further analyze lymph node metastases and multifocality. Results Of the 30,926 cases, 8,697 (28.1%) were mFVPTC. Multifocal tumors occurred with greater frequency in the mFVPTC group compared to the mPTC group (35.4% vs. 31.7%, p<0.01). Multivariate logistic regression indicated that patients with mFVPTC had a 26% increased risk of multifocality (OR = 1.26, 95% CI 1.2–1.4, P<0.01). In contrast, lymph node metastases were nearly twice as common in the mPTC group compared to the mFVPTC group (6.8% vs. 3.6%, p<0.01). Multivariate logistic regression confirmed that patients with mPTC had a 69% increased risk of lymph node metastases compared to patients with mFVPTC (OR 1.69, 95% CI 1.4–2.0, p<0.01). Conclusions Multifocality 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.

Follicular variant papillary thyroid carcinoma in a pediatric population

“…The proportion of each histological DTC subtype in the current pediatric cohort is similar to published adult proportions . Additionally, FVPTCs display intermediate tumor characteristics to PTC and FTC including size, extrathyroidal extension, and nodal positivity as well as intermediate rates of total thyroidectomy and radioiodine utilization . However, although adult studies show FTC has a significantly worse 10‐ and 15‐year survival rate, this was not borne out in this cohort of pediatric patients as all three groups in our study had similar OS and DSS …”

“…[20,21] Additionally, FVPTCs display intermediate tumor characteristics to PTC and FTC including size, extrathyroidal extension, and nodal positivity as well as intermediate rates of total thyroidectomy and radioiodine utilization. [5,16,22] However, although adult studies show FTC has a significantly worse 10-and 15-year survival rate, this was not borne out in this cohort of pediatric patients as all three groups in our study had similar OS and DSS. [16] In adults, three distinct FVPTC subtypes have been described: completely encapsulated, well-circumscribed without complete encapsulation, and infiltrative, each with specific clinicopathologic features.…”

“…The present study shows a trend towards a higher rate of nodal metastases in PTCs compared to FVPTCs that did not reach significance. This study, albeit large for pediatric thyroid patients, might not have sufficient power to show the same statistical difference that has been demonstrated in adults . Additionally, it is not surprising that FVPTCs more often had a total thyroidectomy compared to FTCs and less so than PTCs.…”

“…This study, albeit large for pediatric thyroid patients, might not have sufficient power to show the same statistical difference that has been demonstrated in adults. [22] Additionally, it is not surprising that FVPTCs more often had a total thyroidectomy compared to FTCs and less so than PTCs. We speculate that patients with PTCs underwent primary total thyroidectomy more frequently than those with FTC because cytology is more likely to be definitive/diagnostic for papillary carcinomas than for follicular carcinomas.…”

The age threshold of the 8th edition AJCC classification is useful for indicating patients with aggressive papillary thyroid cancer in clinical practice

“…In addition to age, other risk factors, including large tumor size, lymph node metastasis (LNM) and distant metastasis, have also been shown to be risk factors for a poor prognosis in WDTC [ 11 ]. Singhal et al [ 12 ] revealed that these clinical characteristics vary among pathological subtypes of PTC.…”