Promotion of micrometastasis proliferation in a rat rhabdomyosarcoma model by epidermal growth factor.

Using a rat rhabdomyosarcoma 9-4/0, we investigated the role of epidermal growth factor (EGF) in tumor dissemination. In vitro, we detected high-affinity EGF receptors on tumor cells and stimulation of their proliferation by EGF. When injected iv, EGF-pretreated cells demonstrated an increased capacity to form lung colonies and to invade lymphatic tissue. In vivo, EGF treatment led to increased metastatic spread of subcutaneous tumors. When primary tumors were ablated, and the treatment was given from the time of graft until ablation (seeding step), no effect on metastatic spread was noticed. When treatment was given from the time of ablation until death (growth step), EGF increased the number of lung metastases and of invaded lymph node sites.