Are we ready to use ultrasounds in the clinical assessment of depth of invasion and tumor thickness in oral squamous cell carcinoma? Results from a systematic review, meta-analysis and trial sequential analysis

Objectives: To investigate the accuracy of ultrasound in the quantification of tumor thickness (TT) and depth of invasion (DOI) of oral potentially malignant disorders and oral squamous cell carcinoma. Materials and methods: A systematic review search was conducted in PubMed, Scopus, and Web of Science to answer the PICO question: "What is the correlation and the mean difference between ultrasound and histopathological assessment of tumor thickness and depth of invasion in patients with oral squamous cell carcinoma and oral potentially malignant disorders? The risk of bias was assessed, meta-analysis and trial sequential analysis was conducted on the available quantitative data, followed by trial sequential analysis. Results: Of 2089 results, 48 studies were considered suitable for inclusion. Meta-analysis showed a low heterogeneity for tumor thickness mean difference (I2 = 0.00 %) with an overall standardized mean difference (SMD) of 0.13 (95 % CI:-0.07 to 0.33, p = 0.214). Tumor thickness correlation showed high heterogeneity (I2 = 93.41 %). For depth of invasion, the mean difference had moderate heterogeneity (I2 = 8.98 %) with an overall SMD of 0.27 (95 % CI: 0.06 to 0.48, p = 0.013). However, correlation analysis showed moderate heterogeneity (I2 = 56.22 %). Trial sequential analysis confirmed the tumor thickness results but indicated more studies are required for depth of invasion to meet the required information size. Conclusion: There were no statistically significant differences between the results of ultrasound and histological examination, the clinical use of this device cannot yet be confirmed.