Cystic mucinous adenocarcinoma of the lung. Two cases of cystic variant of mucus-producing lung adenocarcinoma.

Two previously unreported cases of mucus-producing lung adenocarcinoma are presented as uncommon tumors, which are clinicopathologically different from other histologic types of lung adenocarcinoma. The tumors, showing apparently rapid development on chest roentgenograms, were tightly packed with copious mucus and resembled cystic lesions. Because they contained very few cancer cells, and these were only at the periphery, it was impossible to diagnose malignant neoplasms preoperatively through cytologic examination. The present tumors, which we described as cystic mucinous adenocarcinoma, are considered to be a cystic variant of mucus-producing lung adenocarcinoma that expands grossly by storing mucus.