The following literature describes research into the use of human proteins for cancer diagnosis:

The use of Tumor Markers in certain situations is well established. Many of these markers were originally derived from an attempt to develop monoclonal antibodies from crude tissue extracts or cell lines made from specific carcinomas. Many are derived from glycoproteins associated with mucins, and are commonly referred to as carbohydrate antigens (CA). Commonly measured tumor markers include CA15-3, CA-125, CA19-9, CA72-4, CEA, AFP and PSA. These tumor markers are found in the serum of patients with varying tumors. It should be noted that markers are not 100% specific for tumors and suffer from interferences just like any other biochemical analysis.

• Elevated serum CA15-3 levels are reliable prognostic factors for primary breast cancer. CA15-3 has been used to monitor the clinical course of breast cancer patients, and elevation of serum CA15-3 implies that the disease is extended or indicates failure of treatments.
• Most women with ovarian cancer have very high levels of a protein antigen called CA-125 present in their blood stream. While almost all healthy people have CA-125 levels below 35 U/mL of serum, cancer patients may have levels of 10 to 20,000 U/mL CA-125 when they are diagnosed. The level of CA-125 has become a key measurement in monitoring the effectiveness of ovarian cancer treatment.
• CA19-9 is a carbohydrate antigen expressed by a majority of colorectal cancers and is associated with tumor progression. CA19-9 detection in tumor tissue and serum identifies patients at high risk for cancer recurrence and may be useful in selecting patients for additional therapy.
• CA72-4 is a high molecular weight, pancarcinoma human tumor mucin which is a reliable marker for the identification and clinical management of patients with gastric carcinoma. Specific levels of CA72-4 and CA19-9 have been identified which are of value in the follow-up of patients after operation for gastric carcinoma; however, combined measurements of CA72-4 and CA19-9 increase sensitivity and prognostic value of the results.
• Carcino-Embryonic Antigen (CEA) is a tumor associated antigen which has been characterized as a glycoprotein of approximately 200,000 molecular weight. Development of the radio-immunoassay (RIA) made it possible to detect very low concentrations of CEA in blood, body fluids, and in normal and diseased tissues. Results of clinical studies indicate that CEA, although originally thought to be specific for digestive tract cancers, may also be elevated in other malignancies and in some non-malignant disorders. CEA testing can have significant value in the monitoring of patients with diagnosed malignancies in whom changing concentrations of CEA are observed. A persistent elevation in circulating CEA following treatment is strongly indicative of occult metastatic and/or residual disease. A persistent elevation of CEA value may be associated with progressive malignant disease and poor therapeutic response. A declining CEA value is generally indicative of a favorable prognosis and good response to treatment. Patients who have low pre-therapy CEA levels may later show elevations in CEA as an indication of progressive disease. The clinical relevance of CEA monitoring has been shown in the follow-up management of patients with colorectal, breast, lung, prostatic, pancreatic, and ovarian carcinomas. Additionally, studies suggest that pre-operative CEA levels of patients with colorectal, breast and lung carcinoma have prognostic significance. As a point of reference, it has been shown that 99% of healthy subjects have CEA concentrations of less than 5 ng/mL.