Occurrence of fibrin and tissue factor antigen in human small cell carcinoma of the lung.

Fibrin was detected by specific immunofluorescence in tissue obtained from five of six cases of small cell carcinoma of the lung. Dense specific fluorescence was observed in the connective tissue stroma surrounding metastatic tumor nodules and frequently in the scant extracellular stroma surrounding individual viable tumor cells and small tumor cell clusters. When observed by electron microscopy, the fibrin hugged tumor cell plasma membranes and, in some areas, seemed to envelop the cells. Fluorescent staining of tumor cells, but not the stroma, was observed with an antibody to tissue factor. These findings suggest that local activation of coagulation occurs in small cell carcinoma of the lung. Deposited fibrin may contribute to the growth and spread of this particular type of cancer.