PSA Screening May Lead to Overdiagnosis of Prostate Cancer

Researchers from the United States and the Netherlands have reported that prostate specific antigen (PSA) screening results in a long lead time and a high probability of overdiagnosis of prostate cancer. The results of this study were published early online on March 10, 2009 in the Journal of the National Cancer Institute.[1]

Prostate cancer is the second leading cause of cancer death in the United States. PSA testing is becoming routine after the age of 50-55, despite the fact that early diagnosis has not been clearly shown to improve survival. There is currently an ongoing randomized trial (The Prostate, Lung, Colorectal Trial) that has recruited more than 154,000 men, ages 55-74. Patients in this trial were randomized to a screening PSA or usual care arm. While this study is maturing, there are conflicting guidelines on whether or not PSA screening should be performed or not. However, PSA screening every one to four years has become relatively routine for American males. Members of the U.S. Preventive Services Task Force have concluded that there is still insufficient evidence to recommend PSA screening in men 75 years of age or younger.

Overdiagnosis is a huge concern in terms of financial costs, unnecessary treatment, debilitating side effects, and undue anxiety. Prostate cancer grows so slowly that many men end up dying from other causes before the prostate cancer poses a threat. The early diagnosis of a tumor often forces men into treatment that may not prolong their life yet can leave them with side effects such as incontinence and impotence. In addition, the long lead time leaves men living with anxiety about cancer for a disproportionate amount of time. Overdiagnosis also carries a financial burden for patients, insurance providers, and the healthcare system. High PSA levels often lead to unnecessary biopsies and treatment.

In the current study, researchers used three different computer models to estimate lead times and the percentage of overdiagnosed cancers due to PSA screening from 1985-2000.

Using data from the United States, it was estimated that the lead time from a PSA screen-detected cancer to a clinically detected cancer ranged from 5.4 to 6.9 years. Using the U.S. data, it was also estimated that prostate cancer was overdiagnosed (would not have been detected in the normal lifetime) in 23% to 42% of patients. In a separate model, the Rotterdam data predicted a lead time of 7.9 years and overdiagnosis in 66% of patients. In this model the U.S. data showed a lead time of 6.9 years and an overdiagnosis of 42%.

These authors stated: “The precise definition and the population used to estimate lead time and overdiagnosis can be important drivers of study results and should be clearly specified.”

Comments: These and other data strongly suggest that PSA testing in elderly patients will lead to a higher rate of overdiagnosis than in younger patients because their expected life-span is shorter. On a simplistic level, it would appear that younger men (such as between 40-70 years of age) would benefit the most by early diagnosis and treatment while older patients would not benefit as much, especially if they have significant co-morbidities.

Reference:

[1] Draisma G, Etzioni R, Tsodikov A, et al. Lead time and overdiagnosis in prostate-specific antigen screening: Importance of methods and context. Journal of the National Cancer Institute. 2009; 101:374-383.