On May 22, 2012, the US Preventive Services Task Force (USPSTF) issued a statement regarding the use of the serum prostate-specific antigen (PSA) test to facilitate prostate cancer detection. The USPSTF recommended against routine screening in any man of any age, race, or family history of prostate cancer, citing that some screening-vs-observation trials failed to demonstrate a survival benefit. As succinctly summarized by Drs. Aizer and D’Amico in their article and previously described by Catalona, D’Amico, and others, these trials suffer from flaws related to significant non-compliance in the observation arms. One estimate of the rate of screening in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) trial observation arm is as high as 85%. The USPSTF recommendations largely disregarded the data from the Göteborg screening trial, which demonstrated a survival benefit associated with screening and did not suffer the degree of non-compliance in the observation arm that was seen in the USPSTF-referenced trials. Furthermore, other studies that randomized patients to treatment vs observation demonstrate a survival benefit favoring treatment, particularly for patients presenting with localized intermediate- or high-risk prostate cancer. Weighing heavily on these deliberations, but often ignored by those opposed to PSA screening, are the epidemiologic data demonstrating a substantial reduction in the prostate cancer death rate coinciding with the introduction and widespread use of PSA screening in the United States. The introduction of the PSA test into common practice in the early 1990s was associated with a 75% decrease in presentation of patients with advanced disease, and a 40% reduction in prostate cancer mortality. Boorjian et al reviewed the Mayo Clinic surgical experience and found that between the eras of 1988–1993 and 1998–2001, the years associated with widespread introduction of PSA screening, patients undergoing prostatectomy had rates of lymph node involvement that decreased from 9.1% to 1.8%. As Aizer and D’Amico also remark, other expert medical consensus groups do not concur with the recommendations of the USPSTF. Thus, the discourse among those appreciative of these apparent benefits of the PSA test is often centered on whom to screen, not on whether PSA screening is of value.
In their article, “Should All Colorectal Cancer Patients Over Age 60 Be Screened for Prostate Cancer?” Drs. Aizer and D’Amico answer the question, “In which colorectal cancer patients is PSA screening appropriate?” The methodology employed involves estimating the median survival duration of patients with colorectal cancer of a specific stage and using a validated metric for measuring remaining life expectancy that accounts for age and comorbidity in patients with cancer. Life expectancy, the number of years on average remaining in an individual’s lifespan, does not by itself provide information about the statistical distribution around the mean expectancy. The life expectancy and its distribution may clearly impact how vigilantly a patient and his healthcare providers may wish to undergo screening or treatment of other comorbid conditions. For example, Ciecka et al estimate remaining life expectancy of a 70-year-old male in the United States in 1990 at 12 years, but with a standard deviation of 8.2 years. Based on these data and assuming that life expectancy follows a normal distribution, 30% of males who reach age 70 will live beyond 85 years of age and 16% will reach their 90th birthday. In stating that patients with stage III colorectal cancer should not undergo screening until they have a 5-year disease-free interval, the authors estimate when PSA screening is likely to yield a benefit to this population as a whole. If the goal is solely to increase life expectancy, then Aizer and D’Amico make a compelling case that the methodology they describe is a reasonable means to estimate such a benefit.
Other factors may be relevant to the utility of PSA screening in general, and in colorectal cancer patients in particular: (1) The PSA test, if never previously performed, may help to identify men with extensive asymptomatic prostate cancer. In such men, treatment with androgen-deprivation therapy frequently yields a profound improvement in short-term life expectancy and quality of life[7,8]; (2) The PSA test, by itself, does not mandate subsequent biopsy or therapeutic intervention. The test may serve to rule out prostate cancer as a coincident diagnosis and aid in the overall management of newly diagnosed advanced colorectal cancer; (3) PSA is a low-cost test with essentially no morbidity; (4) Men diagnosed with synchronous prostate and rectal cancers are ideally treated in a coordinated manner because the surgical and radiotherapeutic approaches require it; and (5) Some patients with stage IV colorectal cancer and limited hepatic metastases have significant 5- and 10-year survival rates following metastasectomy and systemic therapy, as high as 74% and 69%, respectively.
The main conclusion stressed by the authors deserves reiteration and, in our view, some modification: Once a patient has been appropriately educated by an informed healthcare provider about the possible benefits of PSA screening, then patient preference as part of shared decision making regarding PSA screening should be considered in all cases.
Dr. Catalona is a consultant to, receives honoraria from, and is a research investigator for Beckman Coulter; receives research support from, and is a consultant to, deCODE Genetics; receives research support, and royalties for an experimental PSA test, from Ohmx Corporation; and is an uncompensated consultant to Nanosphere. The remaining authors have no significant financial interest or other relationship with the manufacturers of any products or providers of any service mentioned in this article.
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