72. A 60-year-old man presents with a chronic history of persistent cough, chest pain, and recurrent pneumonia. He denies smoking or consuming alcohol. The patient subsequently dies of sepsis. Autopsy reveals malignant cells that diffusely infiltrate the lung parenchyma. Histopathologic examination of the lung shows well-differentiated, mucus-producing,columnar neoplastic cells lining the alveolar spaces as shown in the image. Neoplastic cells are not found in any other organ. What is the most likely diagnosis?
Large cell carcinoma
Small cell carcinoma
Answer: A Bronchioloalveolar carcinoma
Bronchioloalveolar carcinoma is a primary pulmonary adenocarcinoma originating from stem cells in the terminal bronchioles.
The cells may be columnar and mucus producing or cuboidal and similar to type II pneumocytes.
They tend to grow along the alveolar septa, as depicted in the photomicrograph.
A similar growth pattern may be seen in metastatic adenocarcinomas.
None of the other tumors produce alveolar mucus or display alveolar spaces lined by a columnar epithelium.