Basal STAT3 activities are negatively correlated with tumor size in papillary thyroid carcinomas

Backgrounds: Signal transducer and activators of transcription-3 (STAT3) plays a critical role in promoting survival and cell growth as well as facilitating angiogenesis and metastasis in several cancers. Aim: This investigation focused on evaluation of STAT3 activities in human papillary thyroid cancers (PTC). Methods: STAT3 activities of nuclear extracts of tumor tissue were measured from 35 PTC patients using enzyme-linked immunosorbent assay-based kits. Results: STAT3 activities of PTC tissues were significantly lower than those of surrounding normal thyroid tissues [0.36 (interquartile range 0.24-0.72) vs 0.50 (0.29-1.11) arbitrary units, p<0.01]. We further analyzed the association between STAT3 activity and clinicopathologic factors in PTC tissue. Tumors with size ≥2 cm displayed significantly lower STAT3 activities than those <2 cm [0.25 (0.21-0.37) vs 0.53 (0.37-0.61) arbitrary units, p<0.01]. Notably, tumor size was inversely correlated with STAT3 activities in T1799A BRAF mutation-positive cases (R_s=-0.58, p<0.05), but not mutation-negative cases. Conclusions: STAT3 activities of PTC measured via DNA binding are suppressed in contrast to other human cancers. Tumor size larger than 2 cm is the only clinicopathologic parameter associated with low STAT3 activity. Moreover, tumor size appears inversely correlated with STAT3 activity, specifically in T1799A BRAF mutation-positive cases.