Limitations of the Usefulness of Microvillous Ultrastructure in Distinguishing between Carcinoma Primary in and Metastatic to the Lung

We performed ultrastructural analysis on 70 consecutive patients with solitary cancers in lung with the following histologic classifications: adenocarcinoma (42 cases), bronchioloalveolar carcinoma (13), large cell carcinoma (4), and adenosquamous carcinoma (11). Of these 70 cases, nineteen (13 adenocarcinomas, 4 bronchioloalveolar carcinomas, and 2 adenosquamous carcinomas) contained cell surface microvilli with microvillous core rootlets and/or glycocalyceal bodies. Subsequent clinical followup revealed that three of these 19 cases were actually metastatic colon carcinoma. The remaining 16 patients are currently free of extrathoracic primary disease and are therefore, presumably, primary carcinoma of the lung. Since both primary and metastatic tumors showed cell surfaces with microvilli having core rootlets and glycocalyceal bodies, we conclude that the presence of these ultrastructural features does not always permit the distinction between primary and metastatic adenocarcinoma in lung.