What tumor marker is associated with gastrointestinal tumors?

The most pertinent tumor marker associated with gastrointestinal tumors is CA 19-9. This carbohydrate antigen is specifically associated with pancreatic cancer but can also be elevated in other gastrointestinal malignancies, such as cholangiocarcinoma and gastrointestinal stromal tumors. CA 19-9 is often used in the clinical setting to monitor treatment response and disease progression in patients with these types of tumors.

The choice mentioning the activation of KIT receptor tyrosine kinase relates more to gastrointestinal stromal tumors (GISTs), which are characterized by mutations in the KIT gene. While this is relevant to a specific subtype of gastrointestinal tumors, it does not represent a generalized tumor marker applicable to the broader category of gastrointestinal cancers.

Other options, such as PSA (prostate-specific antigen) and C-inhibin, are associated with different cancers—specifically prostate cancer and certain types of gonadal tumors, respectively—and do not pertain to gastrointestinal tumors. Therefore, the use of CA 19-9 as a tumor marker provides the most relevance in diagnosing and managing gastrointestinal malignancies.