Answer: Micropapillary carcinoma

Histology: An ill-defined nodule is present within the lung, and it demonstrates central elastosis. At the periphery, one sees atypical pneumocytes lining thickened alveolar septa. At high power, one sees tufts of atypical pneumocytes projecting into distorted alveolar spaces. These tufts demonstrate marked cytologic atypia, and lack fibrovascular cores. This is the typical architecture of a micropapillary carcinoma.

Discussion: Bronchioloalveolar carcinoma will feature atypical pneumocytes lining essentially intact, thin alveolar septa. The micropapillary projections seen in the current case should not be present. Atypical adenomatous hyperplasia would feature small (usually less than 5 mm) areas of atypical pneumocytes with minimal cytoplasm lining intact alveolar spaces. The advanced cytologic atypia seen in the current case would not be present. It is always important to consider usual interstitial pneumonitis before diagnosing a pulmonary adenocarcinoma. One may see cytologic atypia, often accentuated on frozen section, in areas of UIP with honeycomb change. In this case, the absence of cilia and the advanced cytologic atypia, along with the absence of other typical features of UIP (such as fibroblast foci, honeycomb change, or temporal heterogeneity of inflammatory changes), exclude this diagnosis.

Micropapillary carcinomas may be seen in a variety of organs. Common sites include the breast, lung, bladder and salivary gland. This morphology is associated with high-stage in all sites.

Reference(s):
– Adv Ant Pathol 2004; 11:297-303.