small cell carcinoma (MONDO_0000402, a Monarch Disease Ontology identifier) can be described as follows. A neuroendocrine carcinoma composed of small malignant cells which are often said to resemble "oat cells" under the microscope. Small cell carcinoma most often affects the lungs. Clinically, this is often a rapidly growing cancer that spreads to distant sites early. Also known as: oat cell cancer, oat cell carcinoma, small cell NEC, small cell cancer, small cell car. (extrapulmonary), small cell carcinoma (extrapulmonary), small cell neuroendocrine carcinoma.