Which tumor marker is often used to diagnose melanoma?

The tumor marker commonly used to diagnose melanoma is LDH, or lactate dehydrogenase. Elevated levels of LDH can indicate the presence of tumors, including melanoma, and are often associated with tumor burden and disease progression. This biomarker can help provide information about the patient's prognosis and the status of the disease, especially in more advanced cases.

Other markers such as CA 19-9, PSA, and CA-125 are associated with different types of cancers and are not typically used for melanoma diagnosis. CA 19-9 is primarily linked with pancreatic cancer, PSA is a marker for prostate cancer, and CA-125 is often used in the context of ovarian cancer. Thus, while these markers are important in their respective areas, LDH is the relevant tumor marker for assessing melanoma.