Tumor Markers in the Diagnosis, Monitoring and Therapy of Pancreatic Cancer: State of the Art

The present review focuses on the utility of serum tumor markers in screening, diagnosis, prognosis and monitoring of pancreatic cancer. Serum determination of all tumor markers studied offers no help in screening or early diagnosis of pancreatic cancer. For diagnosis, blood group-related antigens, in particular CA 19-9, are considered the best indicators of this neoplasm. However, as occurs with other glycoproteic tumor markers, the circulating levels of CA 19-9 are significantly influenced by jaundice, probably because its liver metabolism is reduced. Therefore, the finding of elevated CA 19-9 levels in jaundiced patients has to be evaluated with caution. Since pancreatic cancer recurrences are not susceptible to treatment, the clinical role of widespread use of tumor marker determination in follow-up programs is limited and calls for a critical evaluation.

Cerebrospinal Fluid (Vascular Endothelial Growth Factor) and Serologic (Recoverin) Tumor Markers for Malignant Glioma

BACKGROUND

Clinically useful tumor markers have yet to be identified for malignant glioma. We report on two potential novel tumor markers, vascular endothelial growth factor (VEGF) and recoverin (protein A). VEGF is a highly specific endothelial cell activator that induces angiogenesis both in vivo and in vitro. Our study was designed to assess whether VEGF could be measured in the cerebrospinal fluid (CSF) of patients with cerebral neoplasms and used as a marker of particular tumors. We also studied serum recoverin levels in patients with various brain tumors and compared these to controls. Recoverin is a detectable serologic protein that is expressed in patients with cancer-associated retinopathy, a paraneoplastic syndrome.

METHODS

In the VEGF arm, we used a solid-phase ELISA to determine the levels of VEGF. CSF samples from patients with anaplastic astrocytoma and glioblastoma multiforme (GBM) and with metastatic and nonastrocytic brain tumors were compared with nontumor control samples. In our recoverin study, an immunoenzymetric assay was used to measure the serum recoverin levels patients with glioma and compared with controls.

RESULTS

In the VEGF arm, 89% of samples with malignant astrocytoma and 27% of nonastrocytoma samples had detectable levels of VEGF. VEGF was not detectable in normal CSF samples. The levels of VEGF were significantly higher in high-grade astrocytomas than in nonastrocytic tumors. Recoverin levels were 10-fold higher in patients with recurrent GBM relative to controls. In patients with low-grade glioma, anaplastic glioma, and GBM with no evidence of recurrence, a 3- to 5-fold increase was observed.

CONCLUSIONS

VEGF is detectable in CSF and may be a potential marker for differentiating astrocytic from nonastrocytic tumors. Recoverin is detectable in serum and may be a useful glioma tumor marker, especially for recurrent active disease. These markers may have application for tumor diagnosis, surveillance, and treatment response.

A prospective, blinded analysis of A-PROTEIN (recoverin or CAR protein) levels in pediatric patients with central nervous system tumors

BACKGROUND

Abnormal expression of A-PROTEIN has been identified in a number of tumors including carcinoma of the lung, breast, colon, prostate, and cervix. Brain tumors have been reported to express high plasma levels of A-PROTEIN, suggesting that it may be of significant diagnostic and prognostic value.

PROCEDURE

This prospective study evaluated the sensitivity and specificity of A-PROTEIN levels in pediatric brain tumor patients. Patients included those with newly diagnosed disease pre- and post-surgery, during treatment, during routine follow-up, and at recurrence or progression. A total of 154 A-PROTEIN levels from 54 patients were evaluated.

RESULTS

For patients without evidence of disease, 42% had normal A-PROTEIN levels, 35% were elevated, and 23% were equivocal. For patients with stable disease, 53% demonstrated normal A-PROTEIN levels, 19% were elevated, and 28% were equivocal. For patients with progressive disease, 53% had normal A-PROTEIN levels, 35% were elevated, and 12% were equivocal. The sensitivity was 35% and the specificity was 50%. A correlation of increased A-PROTEIN levels in patients with increased disease in glial tumors was also identified.

CONCLUSIONS

A-PROTEIN levels were not predictive of disease status in children with most brain tumors. However, in patients with glial tumors there was a correlation with increased disease and elevated A-PROTEIN levels. This could represent variability of A-PROTEIN during growth, development, or tumor cell origin and needs further evaluation.

Antibody constructs for radioimmunodiagnosis and treatment of human pancreatic cancer

Pancreatic cancer (PC) is a common disease that is seldom cured. Current approaches to the treatment of PC are not effective because the non-specific nature of both chemotherapy and external beam radiation results in toxicity to normal tissue. Monoclonal antibodies (MAbs) can be used as selective carriers for delivering radionuclides, toxins, or cytotoxic drugs to malignant cell populations. Therefore, MAb-technology has led to a significant amount of research in targeted therapy. Targeted therapy would generally allow the concentration of cytotoxic agents in tumors and would markedly lessen the toxicity to normal tissues, which limits the dosage and effectiveness of systemically administered drugs. A variety of MAbs are being pre-clinically evaluated for the diagnosis and treatment of PC. Novel recombinant antibody constructs hold a promising future in both the diagnosis and treatment of cancer. By genetic-engineering methods, several high affinity antibody fragments with optimum tumor targeting properties, such as higher functional affinity (divalent and multivalent scFvs) and blood residence time (good tumor localization with high radiolocalization index), have been generated. Animal models have permitted the in vivo assessment of these antibody-based reagents, therapeutic/diagnostic radionuclide, radiolabeling conditions, and efficacy of administration regimes. For PC, immunoscintigraphy using MAbs has taken new strides. The use of MAbs and their fragments for radioimmunoguided surgery and therapy of PC has shown encouraging results at preclinical levels and warrants further attention.

Serum diagnostic tests for pancreatic cancer

Serological tests for pancreatic cancer have been criticized too harshly as a result of being tested in inappropriate roles. They are never likely to become sufficiently specific for screening an asymptomatic population unless some way can be found of defining a population with a particularly high risk for the disease. Nor are they appropriate in the investigation of the jaundiced patient. The markers that are carried by secreted mucins seem the most promising and in view of the marked heterogeneity of carbohydrate expression on mucins a combination of tests for two or three carefully selected markers is likely to be better than one. The high cost per test that results from using commercially available radioimmunoassay kits with a short shelf-life can be reduced by using enzyme-linked assays which have a much longer shelf-life. These tests are likely to be of most help in the investigation of non-jaundiced patients with unexplained abdominal pain or weight loss. In this group of patients it seems probable that serological tests will compliment scanning techniques but further studies are needed to assess this.

Biochemical and immunological properties of the human carcinoma antigen CAR-5 defined by the monoclonal antibody BD-5

The monoclonal antibody (MAb) BD-5 reacts with an epitope (CAR-5) expressed in 83% of the gastric carcinomas and in 51% of the ductal pancreatic carcinomas. This MAb reacts also with epithelial cells of colorectal mucosa, but does not react at all with normal adult gastric mucosa or normal adult pancreas. We report the biochemical and immunochemical characterization of CAR-5-bearing molecule. The epitope was found to be carried on a mucin of more than 400 kDa with a density of 1.45 g/ml, metabolically labelled with 35S-sulfate, 3H-glucosamine, 3H-mannose and 35S-methionine. Antigenicity survived metaperiodate oxidation and alkalinization, while it was fully destroyed by pronase or papain. Trypsin, although cleaving the molecule, did not affect its antigenic activity. CAR-5 epitope is thus carried on the protein moiety of a sulfo-mucin. On the basis of its biochemical properties, the antigen was purified by a 3-step procedure, consisting of perchloric acid extraction, molecular sieving on Sepharose CL-4B and affinity chromatography on wheat-germ agglutinin coupled to Sepharose 4B. Cross-competition experiments, together with the chemical properties displayed by the different epitopes, clearly indicate that CAR-5 is different from all previously characterized carcinoma-associated determinants. Cross-DDIRMA experiments performed with different "catcher" and "tracer" antibody combinations showed that CAR-5 epitope may be expressed on the same mucin bearing CA 19-9, MOv2, DU-PAN-2, Lewisa and Lewisb epitopes.