Primary pulmonary adenocarcinoma with enteric differentiation.

A pulmonary neoplasm with cytologic characteristics typical of differentiated small intestinal epithelium is reported. Individual cells showed features suggesting columnar absorptive, goblet, Paneth, and neuroendocrine cell differentiation. Thorough investigation and follow-up for 4 years did not identify a primary tumor other than in the lung. The occurrence of such a neoplasm at this site is evidence for the existence of a common stem cell in the lower respiratory and gastrointestinal tract mucosa.