Morphological and stem cell-like features predictive of stage in medullary thyroid carcinoma

Background: Histological and biological features predictive of staging in medullary thyroid carcinomas remain unknown and can serve as the basis of a grading system in these neoplasms.
Design: We analyzed primary and secondary growth patterns (tubulo-papillary, nested-trabecular, nodular-solid, diffuse), nuclear grade (nuclear abnormalities, including chromatin, nucleolus, pleomorphism and anisokaryosis), stromal reaction, and confluent necrosis in C-cell hyperplasias (CCH, 18), and medullary thyroid carcinomas (MTC,
46) (WHO criteria). Representative samples were evaluated by quantitative RT-PCR and standard in situ techniques for stress-stem cell pathways (telomere PNA-FISH, TERT, TP63, ATF2, BMP4, PTCH1, CCND1, FN1, F13A, CXCR3, MMP10, OCT4, KITLG, MYC, JUN, and FOS), proliferation (Ki-67) and apoptosis (TUNEL assay).
Appropriate controls were run. Fisher’s exact tests and analysis of variance (significant if P<0.05) were used for comparison; significant variables were then selected for discriminant analysis with cross-validation for histological diagnosis, RET genotype, sporadic/familial neoplasms and tumor stage (extrathyroidal 4, lymph node mets 37).
Results: No extrathyroidal extension or lymph node metastasis was observed in the absence of stromal reaction (10/46), lack of necrosis (43/46) or distrophic calcification (39/46) or the presence of pushing edges (21/46) or euchromatin. These aggressive features correlated with the expression of stem cell-like features (TERT, TP63, CD133) that correlated inversely with the presence of apoptotic cells at the tumor periphery and positively with the lack of stromal reaction. TERT, TP63 and CD133 expression correlated positively with ATF2, CXCR3, MYC, FOS, CCND1 (cyclin D1), and FN1 (fibronectin). All other genes showed no statistically significant differences by
histological subtypes and no significant differences were observed for each diagnostic group by the RET genotype.
Conclusions: Locally advanced staging in MTC is defined by expression of stem cell-like (PI3 kinase/AKT -cyclin D1, fibronectin- and NFkB -TERT- pathways) and morphological features (stromal reaction, necrosis, tumor edges, chromatin and dystrophic calcification) that would represent the bases for MTC grading. This grading is independent of RET genotype.