Interestingly, no differences were observed in the invasive characteristics of primary melanomas of HGF+ and HGF+ × [m1m2]+/− strains, with both exhibiting invasion into the dermis and subcutis, indicating factors other than simple invasive activity were responsible for metastasis of HGF+ × [m1m2]+/− melanomas. The gene discussed is HGF; the disease is melanoma.