Prostate Cancer Screening
Early Detection of This Common Malignancy Remains Controversial
Mar 12, 2009
Prostate cancer is the most common non-dermatologic cancer in men over the age of 50 in the United States. Over 200,000 new cases and approximately 30,000 deaths occur each year. (The Merck Manual, 18th Edition 2006:2052-54)
Although there are racial differences in the incidence of prostate cancer, overall men have a 17% chance of developing this disease sometime during their lives. Because prostate cancer typically occurs in older individuals and usually progresses slowly, men only have a three percent risk of dying from this cancer. Thus, it is often said that more men die with prostate cancer than from it.
Under ideal circumstances, cancer screening will detect disease at a stage when intervention decreases morbidity and mortality—that is, when treatment will improve both longevity and quality of life in comparison to untreated individuals who have the same cancer. Several cancer screening protocols have shown clear benefit in this regard.
Unfortunately, prostate cancer varies greatly in its presentation and behavior. Low-grade tumors that are confined to the prostate gland may not cause symptoms; indeed, they might never lead to significant disease. Once they are detected through screening, the side effects of treating these cancers (e.g., urinary incontinence, sexual dysfunction, bowel dysfunction) might outweigh any benefits.
On the other hand, aggressive prostate cancer will eventually spread beyond the gland and cause bone pain. If these cancers are detected only after metastasis has occurred, treatment is of limited value.
Even though management of prostate cancer has improved over the past twenty years, there is scant evidence that intervention increases longevity in the treated population—a statistic that is no doubt influenced by the advanced age of many patients.
Improvements in screening and treatment methods might solidify the argument for routine prostate cancer screening. For now, a great deal of debate surrounds the utility of screening for this particular malignancy.
Methods of Screening for Prostate Cancer
- Digital rectal examination (DRE): A physician inserts a gloved finger into the rectum and palpates the prostate gland. The examination is considered abnormal if the prostate is enlarged, asymmetric, tender, or nodular.
- Prostate-specific antigen (PSA): This blood test measures the level of a protein that is produced by prostate tissue. Most studies recommend a cutoff of 4 ng/ml as the upper limit of normal. Various modifications of this test (age-specific limits, free vs. complexed PSA, PSA density, PSA velocity, and race-specific cutoffs) have all been used in an attempt to increase accuracy.
Limitations of Screening for Prostate Cancer
- DRE: Test interpretation is highly variable between examiners. Reliability is poor: 72-82% of patients undergoing biopsy based on an abnormal DRE will not have cancer, and 25% of cancers detected on biopsy after abnormal DRE are found in a different area than the palpated abnormality.
- PSA: Due to elevations of PSA that occur with non-cancerous conditions (benign hyperplasia, prostatitis, urinary retention, etc.), less than one in three men who have an abnormal PSA will actually have prostate cancer. Additionally, 15-38% of men who do have prostate cancer will have a normal PSA.
(Wilbur J. Prostate cancer screening: the continuing controversy. Am Fam Phys 2008;78(12):1377-84)
Currently, expert recommendations for prostate cancer screening vary. Some organizations state that there is insufficient evidence to recommend for or against PSA or DRE screening. Others recommend offering screening to all men over 50 years of age who are expected to live at least ten years. Still others simply state that screening is unlikely to benefit men over the age of 75.
Until universally-accepted recommendations are forthcoming (two large trials are underway that may help to answer some questions), the decision to screen for—and possibly treat—prostate cancer remains highly individualized.
