This subtype of adenocarcinoma is distinguished by the growth pattern of the tumor cells. The tumor cells use the pre-existing alveolar septa as a framework on which to grow. In this view, the septa are lined by tall columnar cells having large nuclei and cytoplasmic mucin. Sometimes the tumor cells form papillary projections.
Some bronchioloalveolar carcinomas produce abundant mucus.
Tumor cells can often be found floating in the mucus in the involved alveolar spaces.