CEACAM5 and small cell carcinoma: Although—in line with our data—multiple studies showed high rates of CEA positivity in tumor types arising from epithelial tissues, including gastrointestinal adenocarcinomas, medullary carcinomas of the thyroid, adenocarcinomas of the lung, and squamous cell carcinomas of various origins, as well as in small-cell carcinomas, there were also numerous studies suggesting much lower positivity rates in these tumor types.