DNA flow cytometry is a method of measuring the amount of deoxyribonucleic acid (DNA, genetic material)
in tumor cells and the percentage of cells actively replicating.
Purpose
DNA flow cytometric analysis is sometimes done to assess a patient's prognosis. It is used to help the physician determine how the tumor cells are likely to behave. It may also be used to monitor a patient if the tumor is expected to recur.
Description
DNA flow cytometric analysis may be performed on tissue from a biopsy or it may require a sample of blood or body fluid from the patient. If a blood sample is used, it will be separated into its different components and the red blood cells will be removed. If material from a biopsy is used, cells from the solid tissue will be separated from each other. The cells to be analyzed will then be mixed with a dye called propidium iodide that binds tightly to DNA. This dye gives off fluorescent light as the cells pass through the laser beam of the cytometer. The cytometer can also measure other information about the cells, such as their size.
By analyzing the amount of fluorescence that the cells emit, the pathologist can evaluate the DNA content; this is also sometimes referred to as the DNA index or ploidy analysis. It can also determined whether or not the cancer cells are dividing; this is called S-phase analysis. The physician sometimes uses this information to determine the patient's prognosis and choose the most effective treatment.
Preparation
If a biopsy is required, the patient should be prepared for the biopsy as suggested by the physician. Alternatively, a routine blood or body fluid sample may be required. Other special preparations are not usually necessary.
Risks
The risks associated with DNA flow cytometry are limited to those associated with blood or biopsy sample collection.
Normal results
Most cells are normally in a resting, or non-proliferating, phase of the cell cycle. During this time the cells are diploid, meaning they have two copies of each chromosome. Cells duplicate their DNA during what is called S-phase so that they can reproduce, resulting in four copies of each chromosome. The cells rest again until a period called mitosis, when they begin to divide.
Normal DNA flow cytometry results will show that most of the cells are resting and have only two copies of each chromosome. Less than 10% of the cells will be in S-phase. DNA flow cytometry results are usually presented in graphical form for easier analysis. A normal graph will show one large peak of resting cells, followed by a flat area and another smaller peak of cells about to divide.
Abnormal results
Abnormal results will show as several peaks of differing sizes. This means that some of the cells in the sample have extra DNA or an irregular number of chromosomes. An increased percentage of cells may be in S-phase replicating their DNA. An abnormal result does not necessarily mean malignancy; DNA flow cytometry results must be combined with other tests to diagnose malignancy. Interpretation of results is also dependent on the type of tumor being examined. In most types of cancers the presence of cells with irregular amounts of DNA is associated with a poor prognosis, but in some types of cancers, it may indicate a good prognosis.
Javois, Lorette C., ed. Immunocytochemical Methods and Protocols. Totowa, NJ: Humana Press, 1999.
PERIODICALS
Chassevent, A., et al. "S-phase Fraction and DNA Ploidy in 633 t1t2 Breast Cancers: A Standardized Flow Cytometric Study." Clinical Cancer Research 7 (April 2001): 909-17.
Rosen, Shara. "Flow Cytometry: An Underexploited Diagnostic Power." Medical Laboratory Observer 30 (March 1998): 52-8.
