SOX21 and small cell lung carcinoma: Despite these evidence, studies in small cell lung cancers suggest that SOX21 promotes proliferation rather than differentiation (Titulaer et al., 2009) and expression of SOX21 in mouse embryonic stem cells (ESCs) induced the expression of SOX2 and thus maintained their pluripotency (Mallanna et al., 2010; Chakravarthy et al., 2011; Kuzmichev et al., 2012).