SOX2 and small cell lung carcinoma: In terms of cell origin, SOX2 is a transcription factor that maintains the pluripotency of tumor stem cells, studies have found that in PSCCE, SCLC and embryonic esophageal tissue, SOX2 gene is overexpressed and tumor suppressor gene Rb1 is expressed at a low level, but in poorly differentiated squamous cell carcinoma, the opposite is true, suggesting that PSCCE may be derived from embryonic stem cells.