CA242 is related to the sialylated Lewis (a) blood group antigen (CA19-9) and is found on the same mucin complex as CA50 and sialylated Lewis A (CA19-9), but it is chemically and immunologically distinct. CA242 and CA19-9 are co-expressed on different epitopes but on the same carbohydrate macromolecule and similar to CA19-9, CA242 is used as a tumor marker for the early diagnosis of pancreatic cancer. Compared to CA19-9, CA242 has high specificity but lower sensitivity in diagnosing pancreatic cancer and so it is generally used in combination with CA50 or CEA to optimize the assay performance.