Tumor Markers

Cytologic tumor markers are tumor-specific substances in the blood serum or other tissues that can assist in determining the presence or absence of cancer. They can help determine the initial tumor burden in both the primary site and distant sites. Tumor markers can be helpful in monitoring for recurrence. Care should be taken to seek tumor marker information to assist in determining stage.

The most common tumor markers used for prognosis in breast cancer are the estrogen receptor assay (ERA) and the progesterone receptor assay (PRA). Both are steroid hormones receptors. ERA and PRA are used to estimate the potential response to endocrine, or hormone, therapy. They help in the determination of prognosis and the management of breast cancer patients. Pieces of breast cancer tissue are analyzed in the laboratory to determine the ERA and PRA. The presence of estrogen and/or progesterone receptors denotes whether the cancer is growing in the presence of either or both naturally occurring hormones.

Cancer antigen 15-3 (CA-15-3), a tumor associated glycoprotein, is found in the serum. It can be useful in monitoring the presence of metastatic breast cancer and the patient's response to chemotherapy.

Prostate-specific antigen (PSA), a proteolytic enzyme, is used as a screening mechanism for prostate cancer. It can monitor the presence of metastatic disease in patients who have undergone a radical prostatectomy. PSA is not effective for mass screenings because elevated PSAs can also be found in aging patients and in association with benign prostatic hypertrophy (BPH) and prostatitis.

One oncofetal antigen, carcinoembryonic antigen (CEA), has been used for many years to monitor colon, lung, breast, and pancreatic cancers. Rising serum levels of CEA may indicate disease recurrence many months prior to clinical manifestations.

Cancer antigen 125 (CA-125) is a glycoprotein associated with ovarian carcinoma cells. Elevated levels appear in about 75 per cent of ovarian cancer patients and may be associated with tumor burden and recurrence. CA-125 is used to monitor patients for residual or recurrent disease.

Alpha-fetoprotein (AFP) is an oncofetal antigen that is useful in monitoring patients with nonseminomatous testicular cancer and certain types of ovarian cancer. Human chorionic gonadotropin (hCG) is a hormone that can be detected to assess the prognosis and to monitor treatment response in patients with germ cell tumors, breast cancer, choriocarcinoma, and testicular carcinoma.

Flow cytometry has recently become an important clinical test to determine cellular DNA ploidy (the number of sets of chromosomes in a cell) and S-phase (the percentage of cells in active DNA synthesis). In flow cytometry, cells are stained with a special dye and then analyzed in a flow cytometer by using a laser beam to measure the fluorescence of cells. The results are charted in a histogram showing the distribution of DNA in the cells. Results of flow cytometry are helpful to determine prognosis, monitor treatment response, and document tumor recurrence. Tumors demonstrating an abnormal number of chromosomes, such as tetraploidy, polyploidy, or aneuploidy, are more likely to be aggressive than tumors that are diploid (that have the normal two sets of chromosomes). Tumors with a low S-phase have a better prognosis.