The malignant cells are the bland-appearing glandular cells with abundant mucin. The cells are very well-differentiated and are difficult to distinguish from normal glandular cells of the upper airways. However, the presence of these bronchial-type glandular cells in the periphery of the lung is distinctly abnormal and is a useful diagnostic clue. Note how the tumor grows along the pre-existing glandular spaces and does not invade the lung parenchyma. For comparison, note the normal thin and delicate alveolar septae in the lower right corner.
Bronchioloalveolar carcinoma is a specific type of adenocarcinoma.
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