Why Make An Early Diagnosis of Prostate Cancer?
Why would anyone want to be treated for prostate cancer if he believed one of the following "facts"?:
- it has never been proven that an early diagnosis of prostate cancer increases survival;
- there is no need to treat men who have prostate cancer because they do just as well when left alone;
- screening for prostate cancer will detect the tiny microscopic cancers that are found in 30% to 50% of men at autopsy, thus resulting in more deaths from treatment than cure.
However, I like Don Coffey's quote "There is a difference between a fact and a true fact". What are the true facts?
In the United States a man is diagnosed with prostate cancer every 3 minutes and dies from the disease every 15 minutes. In 1994, 38,000 men in the U.S. will die from prostate cancer, approximately 1 out of every 5 who develops the disease; this is similar to the 25% death rate in women who develop breast cancer. And deaths from prostate cancer are on the rise by 2% to 3% per year, because older men are dying less frequently from cardiovascular disease.
To reduce the number of deaths from prostate cancer there are 4 approaches: prevention, early diagnosis, effective treatment of curable disease, and improved management of advanced disease. In the foreseeable future it is unlikely that we will be able to prevent the disease by manipulating environmental or genetic factors or to cure patients with advanced disease while keeping side effects at an acceptable level. Therefore, in order to reduce the number of deaths from prostate cancer we need to diagnose the disease more often when it is still localized to the prostate and treat it effectively.
"FACT" NUMBER 1.
Indeed, no study has demonstrated that an early diagnosis of prostate cancer increases survival. But the true fact is that this issue has never been studied and no one has ever shown that an early diagnosis of prostate cancer does not prolong survival. It has been shown that an early diagnosis of breast cancer is associated with increased survival rates. Breast cancer, like prostate cancer, is an adenocarcinoma that cannot be cured once the disease has escaped the primary organ and it has a natural history not dissimilar from prostate cancer. Today, with serial PSA screening, 70% of men detected with prostate cancer have cancers that are confined to the prostate that can be cured. Thus, it is reasonable to assume that if a proper study is ever performed it is likely that screening studies in prostate cancer will demonstrate improved survival as they have in breast cancer.
"FACT" NUMBER 2.
If prostate cancer is undetected before it has metastasized and is left untreated, it usually takes longer than 10 years to kill the patient. This concept has 3 important implications: 1) the progression of prostate cancer is relatively slow, thus providing a reasonable window wherein the diagnosis can be made and the disease cured before it has spread; 2) if treatment is delayed too long the disease progresses beyond the prostate, undergoes more malignant transformation, and cure is no longer possible; and, 3) efforts at screening for early localized prostate cancer and aggressive therapy should be concentrated only in those men who have a projected life-span longer than 1O years. There is a series from Sweden which is frequently quoted. In this carefully selected series of patients (average age 72 with small well differentiated tumors) in whom watchful waiting was undertaken, at 10 years 13% of the patients were dead and 50% of the patients had progression of cancer to bone or adjacent structures. Thus, although prostate cancer does not kill many men during the first ten years, it does progress in most men causing bone pain or urinary obstruction that requires treatment with castration or hormones. Most patients who experience progression will die during the next 5 years. This may explain why Sweden has one of the highest death rates from prostate cancer in the world.
"FACT" NUMBER 3.
Although small microscopic foci of prostate cancer can be found in 30% to 50% of autopsies performed on men older than 50 years of age, it is unreasonable to assume that today's diagnostic techniques are sensitive enough to detect all of these small foci of tumor. However, in a small minority of men these cancers are detected and in the article "Do I Need treatment?", I discuss how these patients can be identified.
To reduce deaths from prostate cancer we need to diagnose the cancer earlier and treat it effectively. With improvements in the use of PSA testing this should be possible. Today, 70% of men who are identified through sequential PSA screening are found to have localized prostate cancer. In the past, most men with early localized prostate cancer were not identified and the window of curability silently closed before treatment could be instituted. Most of these patients presented late with advanced disease at a time when they were not curable. In the future, this should not occur.
- Walsh, P.C.: Using prostate-specific antigen to diagnose prostate cancer: Sailing in Uncharted waters. Annals of Int. Med. 119:948-949, 1993.
- Walsh, P.C.: Why make an early diagnosis of prostate cancer. J. Urol. 147:853-854, 1992.