Mucinous cystadenocarcinoma of the lung

One case of primary mucinous cystadenocarcinoma of the lung is recorded. The patient was a 67-year-old male with a peripheral mass of the right lung, treated by pneumonectomy. The tumor was made up of fibrous-walled cyst containing abundant mucinous material. Microscopically, it revealed the same morphology as its counterparts arising in other common sites: ovary, appendix and pancreas. The transitional change of the cystic lining from benign features resembling reactive respiratory epithelium to frank malignancy indicated that the tumor had the origin from the lung. This is a very rare intrapulmonary neoplasm that should be differentiated from metastatic lesion and mucinous bronchioloalvolar carcinoma due to different clinical courses and prognoses.