Papillary microcarcinoma of the thyroid gland: current controversies and management

Rethinking Low-Risk Papillary Thyroid Cancers < 1cm (Papillary Microcarcinomas): An Evidence Review for Recalibrating Diagnostic Thresholds and/or Alternative Labels

Background: Recalibrating diagnostic thresholds or using alternative labels may mitigate overdiagnosis and overtreatment of papillary microcarcinoma (mPTC). We aimed at identifying and collating relevant epidemiological evidence on mPTC, to assess the case for recalibration and/or new labels. Methods: We searched EMBASE and PubMed databases from inception to December 2020 for natural history, autopsy, diagnostic drift, and diagnostic reproducibility studies. Where a relevant systematic review was pre-identified, only new articles were additionally included. Non-English articles were excluded. One author screened titles and abstracts. Two authors screened full text articles, performed quality assessments, and extracted data. We undertook narrative synthesis of included evidence (pooled estimates from systematic reviews and single estimates from primary studies). Results: One systematic review of patients undergoing active surveillance found that after 5 years of follow-up, 5.3% (95% confidence interval [CI 4.4-6.4%]) of the mPTC lesions had increased in size by ≥3 mm, and 1.6% [CI 1.1-2.4%] of patients had lymph node metastases. Among 7 new primary studies (including 3 updates on 2 studies included in the systematic review), 1-5% of patients undergoing active surveillance had lymph node metastases after a median follow-up of 1-10 years. One systematic review found that subclinical thyroid cancer incidentally discovered at autopsy is relatively common, with a pooled prevalence of 11.2% [CI 6.7-16.1%] among studies that examined the whole thyroid. Four diagnostic drift studies evaluated the new classification of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). Three studies of cases previously diagnosed as papillary thyroid cancer found 1.3-2.3% were reclassified as NIFTP (reclassifications were from follicular variation of papillary thyroid cancer [FVPTC]). One study of 48 cases previously diagnosed as mPTC found that 23.5% were reclassified as NIFTP. Thirteen reproducibility studies of papillary thyroid lesions found substantial variation in the histopathological diagnosis of thyroid lesions, including FVPTC and NIFTP classifications (no study evaluated mPTC). Conclusions: This review supports consideration of recalibrating diagnostic thresholds and/or alternative labels for low-risk mPTC.

Risk stratification of papillary thyroid microcarcinomas via an easy-to-use system based on tumor size and location: clinical and pathological correlations

Introduction: We aimed to determine whether two clinically accessible parameters, tumor size and location within the thyroid, correlate with clinicopathological features that are predictors of high risk in papillary thyroid microcarcinomas (PTMCs). Materials and Methods: PTMC cases were obtained from the database of the Department of Pathology, Emergency County Hospital, Târgu Mureş, Romania. Four tumor groups were created based on tumor size and location: Group I (≥5 mm, subcapsular), Group II (≥5 mm, nonsubcapsular), Group III (<5 mm, subcapsular), and Group IV (<5 mm, nonsubcapsular) PTMCs. Clinicopathological features and follow-up data were compared by univariate and multivariate analysis. Results: Our study included 164 PTMCs (n=70/20/19/55 in Groups I/II/III/IV, respectively). High-grade morphological features, such as plump pink cells (p=0.010), tumor desmoplasia (p=0.022) and sclerosis (p=0.001), infiltrative tumor borders (p=0.005), positive resection margins (p=0.005), invasion into the perithyroid adipose tissue (p=0.001), irregular nuclear membranes (p=0.004), and pseudoinclusions (p=0.001) were significantly more prevalent among Group I PTMCs. Group IV PTMCs were characterized by a paucity of the above-mentioned morphological features, while Group II and III PTMCs displayed intermediate morphological profiles. Conclusions: Group I PTMCs proved to be associated with more aggressive morphological features and might need a more careful clinical approach.

Clinical management of low-risk papillary thyroid microcarcinoma

Papillary thyroid microcarcinoma (PTMC) is well known to have an indolent nature with an excellent prognosis. Surgery has been the standard treatment during the past several decades, with metastasis or recurrence being exceedingly rare. Active surveillance (AS) is a new risk-adapted approach alternative to surgery that involves just watching, but not giving any treatment unless needed, not addressing the tumor itself. The patients for whom AS is adopted spend their time "with tumors." In follow-up, it is possible that alarming factors such as tumor progression appear, causing anxiety about progression. Furthermore, endless follow-up is needed. However, considering the indolent nature and unfavorable events such as surgical complications caused by surgery, AS is a good management plan for selected PTMC patients. Decision making balancing between the prognosis and unfavorable events is needed for the treatment plan. Consideration of the factors and timing of surgical conversion is also needed. In this review article, how AS should be adopted as a new management option that is an alternative to surgery, which has been the absolute choice of treatment up to recently, is discussed. Concurrently, the characteristics of the two treatment strategies are reviewed, while introducing the background that explains how AS came to attention.