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Looking harder, finding more cancer

Two DMS studies ask: does it help patients?

Two recent studies by a team of researchers at Dartmouth Medical School (DMS) pose questions about screening for two common forms of cancer.

The studies were led by H. Gilbert Welch, Professor of Medicine at DMS and the Veterans Administration (VA) Outcomes Group and colleagues Lisa M. Schwartz, Associate Professor of Medicine and of Community and Family Medicine, and Steven Woloshin, Associate Professor of Medicine and of Community and Family Medicine.

Welch is the author of Should I Be Tested for Cancer? Maybe Not and Here's Why, published in 2004 by the University Of California Press. Together with Schwartz and Woloshin, he has published numerous studies looking at the efficacy of screening. All three are members of the Center for the Evaluative Clinical Sciences at DMS, and primary members of the VA Outcomes Group, working from the VA Medical Center in White River Junction, Vt.

Melanoma diagnosis

Is melanoma being overdiagnosed? Welch and colleagues suggest that an apparent rise in melanoma cases may in fact be a result of overscreening and overdiagnosis.

Dartmouth Medical School researchers
Dartmouth Medical School researchers, left to right, Steven Woloshin, H. Gilbert Welch and Lisa M. Schwartz. (photo copyright Jon Gilbert Fox)

The study, published in the current issue of the British Medical Journal, is based on an examination of skin biopsy rates between 1986 and 2001 among people aged 65 and older in nine geographical areas of the United States. They also measured incidence rates for melanoma for the same population.

The incidence of melanoma of the skin is rising faster than any other major cancer in the United States. In 2002-the most recent year of data-the incidence was about six times that in 1950, but some dermatologists suspect that this rise may reflect more skin biopsies, not more disease. Welch and colleagues noted that death rates from melanoma have remained stable since 1986; what has increased during that time, they report, is the rate of skin biopsies.

Between 1986 and 2001, the average biopsy rate across the nine areas increased 2.5-fold, from 2,847 to 7,222 per 100,000 population, the study found. Over this time, the average incidence of melanoma increased 2.4-fold, from 45 to 108 per 100,000 population.

Even after assuming an increase in the true occurrence of disease, 1,000 additional biopsies were associated with 6.9 extra melanoma cases diagnosed.

Because these extra cases were virtually all early stage cancers and because the overall melanoma death rate remained stable, these findings suggest that the increased incidence of melanoma is largely the result of increased diagnostic scrutiny - that is, skin lesions are being biopsied that would not have been in the past, say the authors. They also suggest that the true occurrence of melanoma has not changed.

Prostate Cancer screening

Lowering the current prostate-specific antigen (PSA) threshold for recommending a prostate biopsy may subject millions of men to unnecessary, potentially harmful medical procedures with no evidence that it will effect prostate cancer mortality rates, according to a new study by the researchers. The study appears in the Aug. 3 issue of the Journal of the National Cancer Institute.

Currently, doctors recommend that men with an "abnormal" PSA level-a level exceeding 4.0 ng/mL-receive a prostate biopsy to test for prostate cancer. However, some men diagnosed with prostate cancer have a PSA level lower than this threshold, prompting some in the medical field to suggest lowering the cutoff to 2.5 ng/mL to possibly detect more cancer cases.

Graph courtesy of H. Gilbert Welch

To examine the implications of this suggestion, the research team examined data for 1,308 men 40 years of age or older with no prior history of prostate cancer who participated in the 2001-2002 National Health and Nutrition Examination Survey - a survey designed to provide national estimates for commonly used laboratory tests. Using this information, they calculated what the impact would be of lowering the PSA cutoff to 2.5 ng/mL if all U.S. men were screened by a PSA test.

They found that if all U.S. men aged 40-69 (those most likely to be screened) were tested using PSA with a 4.0 ng/mL threshold, about 1.5 million of them would have a PSA level abnormally high enough to justify a biopsy. Lowering the threshold to 2.5 ng/mL would call for an additional 1.8 million men to receive biopsies. This group of "abnormal" men would comprise 10.7 percent of all U.S. men between the ages of 50 and 59, and 17 percent of men between the ages of 60 and 69.

To provide perspective, the researchers also examined National Cancer Institute data on the 10-year risk of prostate cancer death-0.3 percent for men aged 50-59, and 0.9 percent for men aged 60-69.

The authors note that no studies to date have focused on the actual effectiveness of PSA screening in terms of cancer mortality, so setting a PSA threshold to maximize the number of potential cases detected may not translate into saving lives. "The problem is that although it is easy to diagnose more prostate cancer, it is not easy to know who has clinically important disease," they write.

If the PSA threshold level is to be changed, the authors argue that it should be set higher, not lower. "Raising the threshold would enhance the net effect of PSA screening by identifying the people at highest risk of clinically significant disease and thereby limiting the number of healthy people harmed," they conclude. "We believe that lowering the PSA threshold would be a mistake."


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Last Updated: 12/17/08