Our results support that C1QL1 can act as a tumor suppressor of BrCa by modulating the C1QL1/HSP90α/VCP-ERS/UPR pathway, implying that the promoter methylation status of C1QL1 or the expression of C1QL1 may represent a potential marker for the diagnosis or prognosis of BrCa. The gene discussed is VCP; the disease is neoplasm.