For molecular subtype, the significant association between serum CK levels and ERBB2+breast cancer was observed (OR = 0.9907, 95% CI = 0.9843–0.9971, P = 0.004), and no significant association was observed between serum CK levels and the other two subtypes of breast cancer (both P = 0.123). The gene discussed is ERBB2; the disease is breast cancer.