Pathology of Metastases

Metastatic disease demonstrates solid tumor patterns similar to that observed at the primary site. The histologic hallmark of Type I disease, cystic spaces with ciliated columnar respiratory epithelium with foci of underlying condensations of malignant cells, is not found in metastatic lesions. In only one of many examined cases of brain metastasis have there been microscopic remnants of cyst and septal elements. There is a tendency toward simplification of the histologic appearance, compared to the primary disease, with an abundance of either the rhabdomyoblastic or spindle cell elements. In a given patient, the microscopic appearances of different metastatic lesions are identical to each other.