ObjectiveTo investigate the correlation between the expressions of bone morphogenetic protein 4 (BMP4) and sma and mad homologue 4 (Smad4) and their clinicopathological features in papillary thyroid carcinoma (PTC).MethodsEighty patients with PTC confirmed by pathology in the Pingdingshan Second People’s Hospital from March 2018 to March 2020 were selected as the research objects, the cancer tissues and adjacent tissues removed during surgery were collected. The mRNA expression levels of BMP4 and Smad4 were detected by real-time quantitative PCR (qRT-PCR). The correlation between BMP4 and Smad4 mRNA expression levels was analyzed by Pearson method. The expressions of BMP4 and Smad4 protein were detected by immunohistochemistry. The correlation between the expressions of BMP4 and Smad4 protein and clinicopathological features of PTC was analyzed.ResultsThe mRNA expression levels of BMP4 and Smad4 in PTC tissues were lower than those in adjacent tissues (P<0.05). Pearson analysis showed that there was a positive correlation between expressions of BMP4 mRNA and Smad4 mRNA in PTC cancer (r=0.660, P<0.05). BMP4 and Smad4 protein were localized in cytoplasm, and the cytoplasm was stained yellow or brown yellow. The results of immunohistochemistry showed that the expression positive rate of BMP4 in cancer tissues of PTC patients was lower than that in adjacent tissues (18.8% vs 97.5%, χ2=101.916, P<0.05), and the expression positive rate of Smad4 protein in cancer tissues of PTC patients was also lower than that in adjacent tissues (11.3% vs 93.8%, χ2=109.173, P<0.05). The expressions of BMP4 and Smad4 protein in PTC patients were correlated with the tumor size, TNM stage, lymph node metastasis, degree of infiltration and multiple foci (P<0.05).ConclusionsThe expression levels of BMP4 mRNA and Smad4 mRNA in PTC tissues are decreased, and the expression of BMP4 protein and Smad4 protein are closely related to tumor size, TNM stage and lymph node metastasis, which may be used as new therapeutic targets.