Diagnosis of pulmonary microvascular metastases by cytologic evaluation of pulmonary artery catheter-derived blood specimens.

Pulmonary microvascular tumor embolization is a recognized cause of respiratory distress in cancer patients that is rarely diagnosed antemortem. Previous studies with relatively few patients have reported high diagnostic yield using wedged pulmonary artery catheter-derived blood samples to evaluate dyspneic cancer patients for possible microembolization. From 1991 to 1993, 21 cancer patients with respiratory distress of relatively acute onset and varying severity who required pulmonary artery catheterization for hemodynamic monitoring were evaluated using this technique. Pulmonary microvascular cytology (PMC) was interpreted as positive for malignant cells in nine of 21 patients presenting with a range of tumor types, including carcinomas of the breast, colon, and pancreas as well as non-Hodgkin's lymphoma. In 11 patients the PMC was interpreted as negative. One case was considered nondiagnostic. Megakaryocytes, noted in most PMC specimens as well as in several samples of simultaneously drawn peripheral blood, may mimic epithelial tumor cells. Immunocytochemical stains for factor VIII and cytokeratins were used to resolve occasional diagnostic dilemmas. Clinical and/or pathologic follow-up information was available for all patients. Diagnostic accuracy was highest for epithelial malignancies. Two false-negative results occurred in patients with metastatic choriocarcinoma and breast carcinoma. Circulating malignant cells in the peripheral blood of a patient with non-Hodgkin's lymphoma led to one false-positive diagnosis. Benign lymphoid elements in PMC generally have a reactive and variable appearance that should not be misinterpreted as lymphoma. We conclude that PMC is a useful tool in the evaluation of dyspneic cancer patients requiring pulmonary artery catheterization for hemodynamic monitoring and its use potentially avoids additional diagnostic procedures.