Serum CA125 levels are decreased in rectal cancer but increased in fibrosis-associated diseases and in most types of cancers.

CA125 is a heavily glycosylated protein and was first identified as an ovarian cancer antigen in 1981 that is recognized by a monoclonal antibody generated by the hybridoma technique. The increased serum CA125 levels detected by the monoclonal antibodies were subsequently developed into a diagnostic or prognostic biomarker for ovarian cancer. Generally, the cutoff value of serum CA125 level is 35U/mL to indicate potential cancer risk. However, the specificity and sensitivity of CA125 are not satisfactory in clinical applications, especially for early diagnosis of ovarian cancer. Moreover, elevated serum CA125 levels have been observed in a variety of cancer and noncancer diseases. In the current study, a total of 41,830 clinical lab test results of serum CA125 levels from healthy individuals and patients with 40 different types of diseases during the past 5 years were retrieved and analyzed. We found that the median values of serum CA125 levels were higher in patients with cirrhosis (52.34U/mL), lung fibrosis (52.04U/mL), nephrotic syndrome (31.24U/mL), and pancreatic cancer (27.06U/mL) than that in ovarian cancer patients (18.61U/mL) with statistical significance (Mann-Whitney test, p<0.0001). Moreover, healthy individuals >65 years old and patients suffering rectal cancer, cerebrovascular disease, and gastritis had significantly low serum CA125 levels compared to that of the healthy individuals. Thus, serum CA125 levels were either increased or decreased in both cancer and noncancer diseases. Based on these data and the accumulating evidence, we proposed that the abnormal serum CA125 levels might be associated with pathological changes in different organs and tissues induced by specific disease.