Significance of freshly cultured fibroblasts from different tissues in promoting cancer cell growth.

The interactions between human cancer cells and primary cultured human fibroblasts without cell-to-cell contact were investigated using double soft-agar culture. Human fibroblasts obtained from different organs were cultured in monolayers and used after the 3rd or 4th passage. In double soft-agar culture, colony formations of cancer cells in the overlayer were stimulated or inhibited by the presence of various kinds of fibroblast in the underlayer. The growth of all cancer cells tested was always stimulated by the presence of fibroblasts obtained from an organ in which cancer cells had already developed, and inhibited by those from skin. However, fibroblast-conditioned media failed to affect cancer cell growth, either in MTT assay or in soft-agar culture. These results suggest that mutual growth reliance exists between human cancer cells and primary cultured fibroblasts by diffusible factors secreted by both cells (paracrine growth) and that mutual growth enhancement occurs between cancer cells and fibroblasts derived from tissues in which cancer cells had originated.