Bronchioloalveolar carcinoma

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It is considered as a variant of pulmonary adenocarcinoma, accounting for about 5% of lung cancers. It is often multifocal, grossly appearing as a pneumonic consolidation. A characteristic feature is its growth along alveolar septa (lepidic growth pattern), without destroying the underlying alveolar architecture. Two subtypes are recognized: the cuboidal non-mucinous type and the mucinous type.

Cytologic diagnostic features (sputum and bronchial washing)

Small glandular clusters
Regular small cells with large cytoplasm
Nuclear hyperchromasia or vescicular nuclei with prominent nucleoli
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Cytologic diagnostic features (FNA and bronchial brushing)

Monotonous cell population
Arrangements in cellular balls, sheets and papillae
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The bronchioloalveolar carcinoma can be hardly distinguished from classic adenocarcinoma on cytologic preparations. Some cases may strictly resemble a papillary thyroid carcinoma, because of the presence of psammoma bodies, occasional nuclear grooves and pseudoinclusions, optically clear nuclei. Clinical history is helpful to exclude a metastasis.

Immunocytochemistry

Cytokeratin 7 +
Cytokeratin 5
Cytokeratin 20
Neuroendocrine markers +-
TTF-1 +

Bronchioloalveolar carcinoma:

Bronchioloalveolar carcinoma. Somewhat cohesive fragment of tumor with tightly packed, minimally pleomorphic nuclei. Also note a few cytoplasmic mucin vacuoles.

Bronchioloalveolar carcinoma. Loosely cohesive tissue fragments with hyperchromatic crowded nuclei mixed with numerous alveolar macrophages.

Bronchioloalveolar carcinoma. Neoplastic epithelium appearing as a cohesive three-dimensional ball-like structure. Note the monotonous appearance of the neoplastic cells.

Bronchioloalveolar carcinoma. Small tissue fragment showing peripherally protruding nuclei (knobby outline) giving the cells a so-called “hobnail” appearance. Note also a benign multinucleated histiocyte on the left.

Bronchioloalveolar carcinoma. A loosely cohesive tissue fragment with monotonous nuclei, vesicular chromatin, and small but prominent nucleoli. Note the deceptive benign appearance of the fragment.