CCND1 and breast cancer: Regarding our findings with CCND1, we predicted that upon ERα inhibition GDNF-RET signaling upregulates EGR1, not only to form a positive feedback loop with GDNF, but also to promote cell proliferation in ERα+ BC patients through EGR1 binding directly to the CCND1 promoter to induce CCND1 transcription.