Oat-cell carcinoma with fibrosis: evidence for release of a growth substance

Recent work demonstrates that transformed cells can produce mitogenic agents capable of stimulating fibroblast proliferation. Also, work with normal cells and tissue has recently demonstrated that, among other cells, macrophages and platelets contain and elaborate potent mitogens capable of stimulating fibroblast proliferation. An unusual oat-cell carcinoma associated with large amounts of fibrous tissue was studied. Short-term cell culture of the pleural fluid was utilized to measure the production of a growth substance. Macrophages were depleted by surface adherence. A potent conditioned medium was obtained, which induced proliferation of BALB/c 3T3 cells and human diploid fibroblasts. This conditioned medium, renewed weekly, was at least as potent as Fibroblast Growth Factor 100 ng/ml every other day. It is concluded that in this human malignancy fibroblast proliferation surrounding the malignant cell is secondary to production of mitogens by the malignant cell.