CLDN5 and oral cavity squamous cell carcinoma: CLDN5 expression has been shown to be reduced in squamous cell carcinomas of the lung (Akizuki et al., 2017), cervical cancer (Zhu et al., 2015), hepatocellular carcinoma (Sakaguchi et al., 2008), oral squamous cell carcinoma (Phattarataratip and Sappayatosok, 2016), breast cancer (Escudero-Esparza et al., 2012), and pancreatic cancer (Jakab et al., 2011).