CPA4 (carboxypeptidase A4) is a zinc-containing metallocarboxypeptidase that cleaves hydrophobic C-terminal amino acid residues, with demonstrated preference for phenylalanine, leucine, isoleucine, methionine, tyrosine, and valine 1. The enzyme is proposed to function in peptide hormone and neuropeptide catabolism 1. However, emerging evidence reveals CPA4's significant role in cancer biology, where it is consistently overexpressed across multiple malignancies including clear cell renal cell carcinoma, non-small-cell lung cancer, anaplastic thyroid cancer, endometrial cancer, hepatocellular carcinoma, and breast cancer 234567. CPA4 promotes cancer cell proliferation, migration, invasion, and stem cell characteristics through activation of key signaling pathways including PI3K-AKT-mTOR 86. In thyroid cancer, CPA4 mediates crosstalk between M2 macrophages and cancer cells, creating a positive feedback loop that enhances tumor progression 4. Additionally, CPA4 promotes cardiac hypertrophy by activating PI3K-AKT-mTOR signaling in cardiomyocytes 8. High CPA4 expression correlates with poor prognosis across multiple cancer types, making it a potential diagnostic biomarker and therapeutic target 325.