A survey of the use of flow cytometry for clinical purposes is given. In the last decade the main clinical application of this technique has been measurements of cellular DNA content for estimation of cell cycle distribution and ploidy studies. A large body of data is now available on the presence of aneuploidy in different malignant diseases. By measurements with high resolution, the demonstration of abnormal cellular DNA content in several types of t u m o r s can be of definite diagnostic value when combined with conventional diagnostic procedures. The prognostic significance of different types of DNA aberrations is so f a r not established. Attempts to monitor cancer treatment by studying altered cell cycle distribution have not been successful, although s o m e applications are of potential value. The main reasons f o r this are the complexity of t u m o r tissue as well as difficulties with interpretation of altered cell cycle distribution caused by drug combinations. For further progress in this field more emphasis on other cell constituents than DNA measured b y flow cytometry is desirable, either as single or as multiparameter measurements.

High‐resolution flow cytometric measurements of cellular DNA content have been performed in 69 patients with transitional cell carcinomas of the urinary bladder. By selective sampling of cells at cystoscopy, mapping of the whole bladder could easily be performed, including the tumor as well as different areas of the surrounding normal‐appearing mucosa. The cell‐cycle distribution showed an increasing fraction of cells with S‐ and G2‐phase content parallel to the World Health Organization (WHO) grade of the tumors, ranging from 1.7% S‐phase cells in normal subjects to nearly 20% in tumors of WHO grade 3. WHO grade 2 tumors could be divided into two populations: (1) diploid, with a cell‐cycle distribution similar to grade 1 tumors and low frequency of infiltration; and (2) aneuploid, with a high rate of infiltration and high fractions of S‐ and G2‐phase cells. Furthermore, the aneuploid tumors could be subdivided into two main classes, one hypertriploid with high frequency of involvement of the surrounding normal appearing mucosa; and one hypotetraploid, with less frequency of such involvement and infiltration. It is concluded that by selective sampling and mapping of the bladder mucosa using flow cytometry, subclassification of this type of tumor can be performed rapidly, giving a reliable measure of the involvement of the bladder in the neoplastic disease and a biologic subclassification based on the type of DNA aberrations.

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