Ultrastructural studies of interactions of B16 melanoma cells and normal mouse skin fibroblasts in the three-dimensional collagen gels in vitro.

In the in vivo system, cancer metastasis is a complex multi-step process. We have utilized an in vitro three-dimensional system to study the initial stages of tumour cell invasion. In this communication, the sequence of events in interactions between B16 melanoma cells and normal mouse skin fibroblasts are described. It is proposed that tumour cells produce a "retractive factor" which induces the underlying fibroblasts to retract so as to facilitate invasion and metastasis.