The non-interventional approach to papillary thyroid microcarcinomas. An "active surveillance" dilemma

Abstract

Background: Recent studies suggest that papillary-thyroid-microcarcinomas (PTMi) and follicular-variant-papillary-thyroid-cancers (FVPTC) are less aggressive overall. Our observations argue against.

Objectives: To assess whether PTMi and FVPTC are indeed low-risk and could be safely followed without intervention.

Methods: We prospectively collected data of subjects with PTC on pathology post-thyroidectomy. Odds ratios (OR) were calculated with Fisher's exact test and differences between means were calculated using Mann Whitney's test.

Results: 696 met inclusion-criteria; 436 had macrocarcinomas (PTMa) and 260 had PTMi. PTMa were statistically significantly more likely to present multifocal [44.0% vs.28.1%], with extrathyroidal extension [22.1% vs.3.4%], lymph nodes involvement [25.5% vs.8.8%] and local invasion [3.1% vs.0.4%] (p < 0.05 for all), but not with distant metastasis [3.4% vs.1.3%, p > 0.05]. Therefore, PTMi measuring down to 0.01 cm, harbored aggressive features. We also identified 174 cases with FVPTC and 522 subjects with non-FVPTC. FVPTC had lower incidence of multifocality [40.1%, vs.60.9%], extrathyroidal extension [8.6% vs.17.4%] and lymphatic involvement [5.2% vs.24.0%], but not distant metastasis or local invasion [p > 0.05 for all]. Therefore, FVPTC measuring down to 0.5 cm, also harbored aggressive features.

Conclusions: PTMi and FVPTC aggressive features are substantial enough to require careful evaluation, independent of their original tumor size before defaulting to just "active surveillance."

Keywords: BRAF V600E mutation; Follicular variant papillary thyroid cancer; Microcarcinoma; Papillary thyroid cancer.