Metastatic adenocarcinoma in the lungs of older laying hens.

As part of a study on ovarian and oviductal adenocarcinomas in older laying hens, 676 commercial egg-laying chickens were necropsied at 4 yr of age. Tumors were identified in 305 (45.1%) of the hens. Grossly visible metastatic tumors in the lungs of a few birds prompted collection of lungs from 228 affected hens for histologic examination. Metastatic adenocarcinomas were identified histologically in the lungs of 42 of the 228 hens (18.4%). The number of tumors and extent of involvement of the lung parenchyma varied from minimal to extensive. Tumor emboli were occasionally seen in pulmonary vessels. Metastatic foci showing expansive or invasive growth were identified. These findings indicate that vascular spread of adenocarcinomas is more common than previously thought in chickens, and the lungs are often involved with metastatic tumors, primarily from the reproductive tract.