Application of the techniques of flow cytometry and image analysis to quantitation of DNA and estimation of events in the cell cycle in human tumors has achieved considerable popularity as a laboratory procedure but so far has failed to be of practical clinical value. As brilliantly summarized by Dr. Ross, retrospective studies have repeatedly shown abnormal DNA values to be of prognostic significance in several organ systems, among them, tumors of the urothelium  and prostate  and, perhaps to a lesser extent, mammary carcinomas .
Unfortunately, few prospective studies with long follow-up have documented in a persuasive fashion the impact of these measurements on treatment. At best, tumor ploidy patterns are considered as ancillary information in treatment protocols, along with a host of other factors. Although DNA tests are often requested by interested oncologists and surgeons, and the results of these tests are provided by competent laboratories, there is limited evidence that tumor ploidy is an important factor in the management of malignant tumors. The laboratory reports are simply filed away as a part of the clinical records.
It is quite possible that information on the significance of DNA studies has not been appropriately disseminated, and therefore, is inaccessible to practicing medical or surgical oncologists, let alone other practitioners. For example, it is nearly routine to measure DNA in samples of mammary carcinoma. Is this information studied? Is it understood? Is treatment modified as a consequence of the DNA studies? More importantly, perhaps, is the information shared with the patient?.
DNA Analysis Has Great Clinical Significance in Some Tumors
Ironically, in some areas, DNA ploidy measurement could be of great clinical significance. For example, the treatment of prostatic carcinoma could be significantly influenced by the use of DNA data. Several independent sources have provided reliable evidence that diploid prostatic cancers have a relatively indolent course and progress very slowly [4-6]. It is quite likely that patients with such tumors, particularly those of low stage, could be observed or treated conservatively with hormonal therapy without any significant loss in long-term survival. In fact, the quality of life of the patients not treated by radical extirpation or massive radiotherapy of the prostate would very likely be much superior to that of treated patients.
There also is evidence that DNA ploidy measurements may have a major impact on the behavior of high-stage and even metastatic prostatic cancers. Tumors in the diploid range and some tumors in the tetraploid range progress slowly and show a better survival than aneuploid tumors [7,8]. On the other hand, aneuploid prostatic carcinomas are likely to progress rapidly, and therefore, require rapid, aggressive treatment.
Despite these findings, there is no evidence that DNA analysis has had a major impact on the ever-increasing frequency of radical prostatectomies . One wonders why this is so, particularly in the absence of hard data on clinician's attitudes. It is likely that physicians harbor significant lingering doubts as to the reliability and clinical value of the test, particularly in the absence of guidelines from major medical centers.
What DNA Ploidy Measurement Does and Doesn't Tell Us
What does the information from DNA analysis tell us? Measuring DNA and cell cycle events in a tissue or cell sample provides only coarse information on the genetic make-up of the tumor. The information is not of diagnostic value because, as Dr. Ross emphasizes, benign tumors can be aneuploid and malignant tumors diploid . It does tell us that, in some malignant tumors, the changes in the cell genome have been slight or none (diploid tumors) or marked (aneuploid tumors). Interestingly, diploid solid malignant tumors occurring in adults that retain a complete or nearly complete genome have, on the whole, a less threatening behavior than aneuploid tumors. Although the proof is lacking, it appears likely that, in many but not all diploid tumors, the mechanisms regulating cell proliferation are relatively intact. Oddly enough, as Dr. Ross stresses, small cell diploid tumors of childhood respond poorly to therapy, whereas aneuploid tumors do much better.
There are limits to what we can infer from DNA ploidy measurement, however. For example, DNA analysis does not tell us anything about possible genetic changes, such as activation of tumor-promoting genes (oncogenes) or mutation of tumor-inhibitory genes (anti-oncogenes). Expensive, time-consuming molecular studies are required to ascertain such genetic changes. Yet, curiously enough, when comparative molecular genetic studies are conducted, the morphology of many tumors and their DNA profile correspond closely to each other, and correlate with molecular genetic data and tumor behavior . Such studies are still uncommon but ultimately may lead to persuasive results of clinical value.
Unfortunately, many of the molecular genetic studies are conducted in a clinical vacuum without the close cooperation of clinicians and pathologists. Consequently, data on the long-term clinical significance of genetic changes often are lacking. Also, the results of some of these studies that receive a great deal of publicity may prove to be only partially true or totally useless with the passage of time.
Closer Cooperation Among Investigators Needed
It appears to this writer that a better cooperation among the various interested investigators may be helpful in addressing some of the problems related to DNA ploidy and cell cycle analysis and its clinical significance. DNA measurements are easily accessible, relatively inexpensive, and useful in some clinical situations. They should receive wider attention among clinicians. To ascertain the true biologic significance of these DNA changes may require many years of coordinated prospective studies by pathologists, molecular biologists, and interested clinical parties.