Since, based on an analysis of mRNA levels, the overexpression of GFRɑ1, but not RET, in the breast cancer has been shown to be associated with cancer metastasis and invasion [4], it is possible that RET-independent, GDNF, and GFRɑ1-dependent events play a significant role in the tumor malignization process. This evidence concerns the gene GDNF and breast cancer.