Neha Vapiwala, MD
Ultima Vez Modificado: 5 de marzo del 2007
Dear OncoLink "Ask the Experts,"
In the "Ask the Experts" article entitled Prognosis After Prostatectomy, a woman asked whether her family physician had erred by not routinely screening her husband for the past 10 years with a PSA.
The answer given was that he should have had annual PSA testing in conjunction with a digital rectal exam starting at age 50-55. There was no mention of the controversy surrounding this approach in the medical community or the lack of hard data to support this approach (though some data is now emerging). Please elaborate on this.
Neha Vapiwala MD, Senior Editor for Oncolink, responds:
Prostate-Specific Antigen (PSA) is a protein that is normally made by the prostate. It circulates in the blood and thus is fairly easy to measure using a blood test. Due to the fact that many prostate cancers produce a markedly elevated level of PSA, it has been suggested since the mid 1980s that blood levels of PSA be checked to screen for prostate cancer. Unfortunately, prostate cancer is not the only condition that elevates levels of PSA. In fact, the term "prostate-specific" in prostate-specific antigen means that this antigen is specific to the prostate; it is not specific to cancer of the prostate. For example, a common condition called benign prostatic hypertrophy (BPH) can also raise PSA levels, as can a simple infection of the prostate (prostatitis). In addition, serum PSA levels are elevated for anywhere from 6 to over 48 hours after ejaculation, and can be elevated for as long as several weeks after prostate biopsy or surgery. For these reasons, an elevated serum PSA level does not always automatically signify cancer. This has led to controversy surrounding the issue of PSA screening. While an abnormal PSA may help diagnose some cancers earlier than they would have been found otherwise, it may also lead to unnecessary tests and biopsies in a large number of men who do not have cancer.
Furthermore, it has not been proven that screening for prostate cancer actually saves lives in the end. While a greater number of cancers may be detected, there is a higher likelihood of finding cancers that would never become clinically significant (i.e. cause symptoms or death). As many as 70% of men have been found to have the incidental finding of prostate cancer at autopsy, yet only 2% to 3% of men in the same age group have clinically evident prostate cancer, implying that the majority of prostate cancers are, and remain, asymptomatic.
A PSA level below 4.0 ng/ml is considered normal, but not everyone with a higher PSA level will have cancer. A level between 4 and 10 ng/ml has a positive predictive value of approximately 28% to 35% (Catalona et al, Smith et al). This means that only 28% to 35% of the men who are detected to have a PSA level this high will actually have cancer (which means that 65% to 72% will have a false positive test). Similarly, as many as 30% of men who do have prostate cancer may not have it picked up by PSA screening (Mettlin et al). However, as PSA levels climb above 10 ng/ml, the likelihood of cancer increases.
The American Urological Association and the American Cancer Society both recommend that all men 50 years of age or older undergo routine screening of PSA every year, and that men with a family history of prostate cancer at an early age and/or of African-American descent undergo PSA screening annually starting at age 40. The U.S. Preventive Task Force and the American College of Physicians, however, do not recommend routinely using PSA to screen for prostate cancer. Rather, they recommend that physicians describe the potential benefits and harms of testing, and individualize the decision of whether or not to check PSA.
In an article on this very topic, Drs. Burack and Wood recommend that patients be aware of the following information in order to make a well-informed decision on prostate cancer screening:
Burack RC, Wood DP Jr. Screening for Prostate cancer: the challenge of promoting informed decision making in the absence of definitive evidence of effectiveness. Medical Clinics of North America 83: 1423-42, 1999.
Catalona WJ, Hudson MA, Scardino PR, et al: Selection of optimal prostate specific antigen cutoffs for early detection of prostate cancer: Receiver operating characteristic curves. J Urol 152:2037-42, 1994.
Mettlin C, Jones G, Averette H, et al.: Defining and updating the American Cancer Society guidelines for the cancer-related checkup: Prostate and endometrial cancers. CA Cancer J Clin 43:42-46, 1993.
Mettlin C, Murphy GP, Babaian RJ, et al: The results of a five-year early prostate cancer detection intervention. Investigators for the American Cancer Society National Prostate Cancer Detection Project. Cancer 77:150-9, 1996.
Montie JE, Wood DP Jr, Pontes JE et al: Adenocarcinoma of the prostate in cystoprostatectomy specimens removed for bladder cancer. Cancer 63:381-5, 1989.
Sakr WA, Grignon DJ, Crissman JD, et al: High grade prostatic intraepithelial neoplasia and prostatic adenocarcinoma between the ages of 20-69: An autopsy study of 249 cases. In Vivo 8:439-43, 1994.
Smith DS, Humphrey PA, Catalona WJ: The early detection of prostate carcinoma with prostate specific antigen: The Washington University experience. Cancer 80:1852-6, 1997.Imprima English