Slide A
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.

Slide B
Some bronchioloalveolar carcinomas produce abundant mucus. Tumor cells can often be found floating in the mucus in the involved alveolar spaces.