AGR2 and neoplasm: (111) designed a hexapeptide based on the combination of AGR2 with the largest subunit of RNA Polymerase II (RNAPII) in a peptide motif dependent manner, which interfered with RNAPII by competitively destroying the AGR2-RNAPII complex, leading to RNAPII dysfunction and accompanied by the activation of DNA damage response in early tumor lesions, and proved to be effective in the treatment of breast cancer.