High-risk morphological features are less prevalent among small (<5mm) papillary thyroid microcarcinomas compared to larger (≥5mm) tumors: a study of 206 cases

Introduction: Papillary thyroid microcarcinoma (PTMC) is defined as a PTC measuring 1 cm or less, incidentally discovered. The aim of this study was to determine whether small (<5mm) tumors by contrast with large (≥5mm) ones are less frequently associated with high-risk morphological features, predictive of tumor aggressiveness.
Materials and methods: All consecutive PTMC cases registered at the Department of Pathology, Târgu-Mureş Emergency County Hospital between 2003-2014 were reviewed. The following have been assessed: tumor size, subcapsular versus nonsubcapsular location, extrathyroidal extension/invasion into the perithyroidal adipose tissue, multifocality, resection margins, lymph node involvement, histological variant, tumor border, stromal reaction (fibrosis/desmoplasia/sclerosis), presence of plump pink cells, nuclear features of the tumor cells, intratumoral lymphocytic infiltrate, multinucleated giant cells, psammoma bodies and stromal calcification. The cases were split in two categories: small (< 5mm) and large (≥ 5mm) PTMCs and the pathological features were evaluated in comparison.
Results: Our study included 206 cases, 91 large and 115 small PTMCs, respectively. Large PTMCs were significantly associated with the presence of plump pink cells (p=0.002), well developed PTC nuclear features (p=0.003), stromal reaction (fibrosis/desmoplasia/sclerosis) (p<0.001), infiltrative tumor border (p=0.011), subcapsular location (p<0.001), positive resection margins (p=0.022), stromal calcifications (p<0.001) and intratumoral multinucleated giant cells (p<0.001). Small PTMCs were generally well circumscribed and nonsubcapsular.
Conclusions: Our results have shown that small (<5mm) PTMCs are less frequently associated with high-risk morphological features, predictive of tumor aggressiveness compared with large (≥5mm) tumors and could thus be considered as low-risk cancers.