Among the possible explanations for tumor development in c-kit null rats, there are two that deserve particular attention: 1) the lack of a "protective" effect due to the absence of the c-kit tyrosine kinase receptor which may contribute to a disruption in the cell-cell communication between c-kit expressing mammary epithelial cells and SCF-expressing fibroblasts, or mast cells and fibroblasts, and 2). Here, NTRK1 is linked to neoplasm.