Photomicrographs of tumor cell colonies (3a-e) and fibroblasts immunostained for FGF-7 (3f). In the absence of heparin, breast cancer cells co-cultured on a monolayer of fibroblasts generally produced irregularly shaped large clusters of tumor cells (3a). When heparin was added to the co-culture system, the tumor cells generally formed compact clusters (3b). FGF-7 added to the co-culture system resulted in large glandular-like structures composed of a peripheral rim of compact tumor cells and a central core of plate-like epithelial cells (3c, d). Heparin completely reversed the effects of FGF-7 and produced small compact clusters of darkly staining tumor cells (3e). Immunostaining for FGF-7 (3f) confirmed the abundant presence of FGF-7 (pink stain) on the membrane of the fibroblasts. Toluidine blue stain (3a-e).