Clinical features

The lung receives all of the cardiac output and is a common site of metastasis. In many cases, the lung is the only site of distant metastasis. Autopsy studies have revealed that as many as 50% of patients dying of cancer have lung metastases and metastatic tumors to the lung are three times more common than primary lung cancers. However a practicing pathologist renders a diagnosis of bronchogenic cancer more often than metastatic cancer involving the lung because most patients with metastatic disease are not biopsied. Virtually any carcinomas or sarcomas arising from any body site can spread to the lung via hematogenous or lymphatic channels, but the most common malignancies metastatic to the lung are breast, colon, pancreas, stomach, melanoma, kidney, and sarcomas. In addition, malignant tumors from adjacent sites, such as the esophagus or mediastinum, can secondarily involve lung by contiguous spread.

Recognizing and correctly diagnosing metastatic and secondary malignancies in lung cytologic preparation is critical for subsequent patient management. Often the clinical radiographic setting strongly suggests that the tumor in the lung is metastatic rather than primary lung disease. Lung cytology specimens containing malignant cells morphologically similar to prior surgical specimens from a remote site are strong evidence of metastatic disease. Even in a setting where metastatic disease is suspected and a primary tumor is known, a pathologic diagnosis may still be sought by a clinician to confirm metastatic disease. Thus every effort should be made by the cytopathologist to differentiate metastatic disease from a primary lung malignancy.