Micrometastasis in resected lungs of lung cancer patients

In order to find causes for recurrence and/or metastasis after removal of human lung cancer, microscopic metastasis was examined histologically in the seemly unaffected areas of the lung in primary lung cancer patients. In 55 of 116 cases (47%), microscopic metastases were found in the areas of the lung which looked normal. These micrometastases were localized in 22 cases and disseminated in 33 cases. The sites where tumor cells were growing were identified in lung tissue as blood vessels, lymphatics, and aerial spaces, although it was difficult to identify a few cases. The incidence of microscopic metastases was significantly lower in the lungs of the group in which the diameter of a tumor was less than 3 cm, than those in which the diameter was more than 3 cm. In addition there was a significant decrease in the rate of microscopic spreads in the specimens without lymph node involvement as compared to those with lymph node involvement. The rate of postoperative recurrence and/or metastases was significantly high in the cases with micrometastasis compared to those without, suggesting that most of the microscopic spreads would become distinct tumors if unresected.