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zoom RSS 前立腺癌のスクリーニングの有効性に疑問/PSA

<<   作成日時 : 2009/03/21 01:03   >>

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 前立腺癌のスクリーニングについては20年間論争が続いている。多くの臨床医は、早く腫瘍を見つけて、それを切り取ることが、前立腺ガン治療の最もよい可能な方法であると信じてきた。スクリーニングに対する批評家は、多くの前立腺腫瘍がとてもゆっくり成長するので、患者は、腫瘍が脅威になる前に他の原因で死ぬ可能性があると主張してきた。早期治療が腫瘍を放置するより多くの損害を引き起こす可能性があると言う。
画像 2つの大きな待望の研究結果は、前立腺ガンのスクリーニングがほとんどないし全然延命の利点を提供せず、どのような明らかな利益もなく苦痛と衰弱、高価な治療をもたらしている可能性があることを示している。水曜日に発表された知見は批評家のスタンスを支持する。
 しかし、医師や患者は用心深い。
 研究の一つからは、76,000人の米国人に対するスクリーニングから延命効果は全く無かった。2つ目の報告は、162,000人の欧州での研究で死亡が20%低下した結果だったが、死亡数が少ないため統計学的にかろうじて有意差が出たと言う。
 欧州からの報告では、1,400人のスクリーニングから1人の命を救うために48人のガン治療が必要であった。
 対照的に、乳がんでは2人の命を救うために11人の女性の治療をしなければならないが、副作用はずっと厳しいというわけではない。女性は再建手術で永久的な効果が得られるが、男性は長期のインポテンツと尿失禁を伴う。
 スクリーニングを真剣に考慮したほうがよいのは、高い危険性のある2グループ、アフリカ系アメリカ人男性と前立腺ガン家族歴を持つ人である
 国立がん研究所によると約186,000人の米国人が今年前立腺ガンと診断され、約28,660が死亡すると推計されている。
 スクリーニングとして、前立腺固有の抗原PSAと直腸診がある。1992年以来、PSAテストが導入された5年後に、前立腺ガンによる米国の死亡率は1年あたり約4%低下した。
 現在は、どの組織も定期スクリーニングを推奨していない。米国癌学会と泌尿器科学会は50才以上で10年以上の余命がある人には年1回の検査をオプションとしている。議会が設立した米国予防策部門タスク・フォースは、去年の秋に、75才以上の人がテストを与えられるべきでないことを述べたガイドラインを出した。
 2つの研究とも中間報告であり、より確定的な結果を出すための研究が続行される。7-10年の経過観察は十分ではなく、前立腺癌は成長が遅く15-20年の後に死亡にいたる。治療を受ける人のQOLの分析も重要である。
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Studies cast doubt on prostate cancer screenings
The tests rarely save lives, researchers say, and treatment can cause more harm than the potential tumor.
By Thomas H. Maugh II
March 19, 2009
http://www.latimes.com/news/nationworld/nation/la-sci-prostate19-2009mar19,0,2276723.story

Whether to screen men for prostate cancer has been a controversial topic for at least 20 years. Many clinicians have believed that finding a tumor early and cutting it out is the best possible way to treat prostate cancer, just as it is for most tumors.

Critics of the screening have argued that many prostate tumors grow so slowly that the patient is likely to die of other causes before the tumor becomes a threat. They contend that early treatment can cause more damage than leaving the tumor alone.

Now, two major and long-awaited studies show that screening men for prostate cancer provides little or no benefit in saving lives and can lead to painful, debilitating and expensive medical treatments without any obvious benefit.

The newest findings, released Wednesday, would seem to support the stance of the critics. But doctors -- and patients -- are cautious. And though the new results may seem definitive, experts say they're still not clear-cut enough to recommend against screening for prostate cancer. As such, the decision to screen is likely to remain one made by doctor and patient, with both unsure whether or not the test is prudent or risky.

The first report, on an American study of 76,000 men, found no survival benefit from screening. The second report, on a European study of 162,000 men, found a 20% reduction in deaths -- which was only barely significant statistically because of the small number of deaths on which it was based. Both reports were published online in the New England Journal of Medicine.

Even with the reduction found in the European trial, it was necessary to screen 1,400 men and treat 48 cancer cases to save one life.

"What the European study tells us is that, if you are a man who chooses screening, you are 47 times more likely to be harmed . . . than to have your life saved," said Dr. Otis W. Brawley, chief medical officer of the American Cancer Society.

In contrast, only 11 women with breast cancer must be treated to save two lives, he said, and the treatment's side effects are much less severe. Men suffer long-term impotence and urinary incontinence, while women can get reconstructive surgery and suffer fewer permanent effects.

"If a man is really worried about prostate cancer, he should take that statistic under advisement and decide to get screened," Brawley said. "If he is not worried, he should decide to avoid screening."

The bottom line is that the studies "are not necessarily going to change practice much in the United States," said Dr. Howard Sandler of Cedars-Sinai Medical Center, a spokesman for the American Society of Clinical Oncology.

The papers "don't tell patients anything different from what we have been telling them," which is do it only if you are very concerned, added biostatistician Ruth Etzioni of the Fred Hutchinson Cancer Research Center in Seattle. "When you have a large controlled trial like these, it is usually the final word . . . conclusive. These are very unsatisfying."

Men more likely to seriously consider screening would be African American men or those with a family history of prostate cancer, two groups who face a higher risk of the disease. About 186,000 American men will be diagnosed with prostate cancer this year, and an estimated 28,660 will die from it, according to the National Cancer Institute.

Screening for the disease usually involves a prostate-specific antigen, or PSA, blood test and a digital rectal exam, in which a physician manually feels the prostate for any abnormalities. In the United States, a normal level of PSA is considered to be 4. Higher levels generally indicate the presence of a tumor, and rising levels indicate an aggressive tumor.

Since 1992, five years after the PSA test was introduced, U.S. death rates from prostate cancer have declined about 4% per year. Some attribute the decline to the test, while others say it is due to better treatment regimens.

No group currently recommends routine screening. Both the American Cancer Society and the American Urological Assn. recommend that men 50 years and older simply be offered the option of an annual test if they have a life expectancy of more than 10 years.

The U.S. Preventive Services Task Force, established by Congress to make recommendations about preventive care, issued guidelines last fall stating that men older than 75 should not be given the test. The group said there was not enough evidence of efficacy to produce guidelines for younger men.

The two studies released Wednesday in the journal and at the Stockholm meeting of the European Assn. of Urology were designed to give a definitive answer about the value of such screening. Both are interim reports, and researchers will continue to follow the subjects for several more years in hopes of producing a more definitive conclusion -- that is, results with less of a discrepancy.

The seven to 10 years that patients have been followed "is not long enough," Sandler said. "We know prostate cancer has a long natural history and that deaths can take 15 to 20 years after diagnosis."

But even if the studies were to be extended by an additional five years, they are not going to produce "a stunning result," Etzioni said, because the studies are unlikely to show the dramatic lowering in death rate that researchers had hoped for.

The teams promise more papers in which they will analyze the treatments and the quality of life for those who undergo therapy. Those results are likely to be more informative and "will color which way I would lean very heavily," said Dr. Glen Justice, director of MemorialCare Cancer Center at Orange Coast Memorial Medical Center in Fountain Valley.

thomas.maugh@latimes.com
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Published at www.nejm.org March 18, 2009 (10.1056/NEJMoa0810696)

Mortality Results from a Randomized Prostate-Cancer Screening Trial


Gerald L. Andriole, M.D., Robert L. Grubb, III, M.D., Saundra S. Buys, M.D., David Chia, Ph.D., Timothy R. Church, Ph.D., Mona N. Fouad, M.D., Edward P. Gelmann, M.D., Paul A. Kvale, M.D., Douglas J. Reding, M.D., Joel L. Weissfeld, M.D., Lance A. Yokochi, M.D., E. David Crawford, M.D., Barbara O'Brien, M.P.H., Jonathan D. Clapp, B.S., Joshua M. Rathmell, M.S., Thomas L. Riley, B.S., Richard B. Hayes, Ph.D., Barnett S. Kramer, M.D., Grant Izmirlian, Ph.D., Anthony B. Miller, M.B., Paul F. Pinsky, Ph.D., Philip C. Prorok, Ph.D., John K. Gohagan, Ph.D., Christine D. Berg, M.D., for the PLCO Project Team

Editor's note: Do the benefits of PSA screening outweigh the risks? Watch video of a roundtable discussion, participate in a poll, and contribute your comments in our Clinical Directions feature ― Screening for Prostate Cancer. Commenting closes April 1, 2009.

ABSTRACT

Background The effect of screening with prostate-specific–antigen (PSA) testing and digital rectal examination on the rate of death from prostate cancer is unknown. This is the first report from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial on prostate-cancer mortality.

Methods From 1993 through 2001, we randomly assigned 76,693 men at 10 U.S. study centers to receive either annual screening (38,343 subjects) or usual care as the control (38,350 subjects). Men in the screening group were offered annual PSA testing for 6 years and digital rectal examination for 4 years. The subjects and health care providers received the results and decided on the type of follow-up evaluation. Usual care sometimes included screening, as some organizations have recommended. The numbers of all cancers and deaths and causes of death were ascertained.

Results In the screening group, rates of compliance were 85% for PSA testing and 86% for digital rectal examination. Rates of screening in the control group increased from 40% in the first year to 52% in the sixth year for PSA testing and ranged from 41 to 46% for digital rectal examination. After 7 years of follow-up, the incidence of prostate cancer per 10,000 person-years was 116 (2820 cancers) in the screening group and 95 (2322 cancers) in the control group (rate ratio, 1.22; 95% confidence interval [CI], 1.16 to 1.29). The incidence of death per 10,000 person-years was 2.0 (50 deaths) in the screening group and 1.7 (44 deaths) in the control group (rate ratio, 1.13; 95% CI, 0.75 to 1.70). The data at 10 years were 67% complete and consistent with these overall findings.

Conclusions After 7 to 10 years of follow-up, the rate of death from prostate cancer was very low and did not differ significantly between the two study groups. (ClinicalTrials.gov number, NCT00002540 [ClinicalTrials.gov] .)

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Published at www.nejm.org March 18, 2009 (10.1056/NEJMoa0810084)

Screening and Prostate-Cancer Mortality in a Randomized European Study

Fritz H. Schröder, M.D., Jonas Hugosson, M.D., Monique J. Roobol, Ph.D., Teuvo L.J. Tammela, M.D., Stefano Ciatto, M.D., Vera Nelen, M.D., Maciej Kwiatkowski, M.D., Marcos Lujan, M.D., Hans Lilja, M.D., Marco Zappa, Ph.D., Louis J. Denis, M.D., Franz Recker, M.D., Antonio Berenguer, M.D., Liisa Määttänen, Ph.D., Chris H. Bangma, M.D., Gunnar Aus, M.D., Arnauld Villers, M.D., Xavier Rebillard, M.D., Theodorus van der Kwast, M.D., Bert G. Blijenberg, Ph.D., Sue M. Moss, Ph.D., Harry J. de Koning, M.D., Anssi Auvinen, M.D., for the ERSPC Investigators

Editor's note: Do the benefits of PSA screening outweigh the risks? Watch video of a roundtable discussion, participate in a poll, and contribute your comments in our Clinical Directions feature ― Screening for Prostate Cancer. Commenting closes April 1, 2009.

ABSTRACT

Background The European Randomized Study of Screening for Prostate Cancer was initiated in the early 1990s to evaluate the effect of screening with prostate-specific–antigen (PSA) testing on death rates from prostate cancer.

Methods We identified 182,000 men between the ages of 50 and 74 years through registries in seven European countries for inclusion in our study. The men were randomly assigned to a group that was offered PSA screening at an average of once every 4 years or to a control group that did not receive such screening. The predefined core age group for this study included 162,243 men between the ages of 55 and 69 years. The primary outcome was the rate of death from prostate cancer. Mortality follow-up was identical for the two study groups and ended on December 31, 2006.

画像Results In the screening group, 82% of men accepted at least one offer of screening. During a median follow-up of 9 years, the cumulative incidence of prostate cancer was 8.2% in the screening group and 4.8% in the control group. The rate ratio for death from prostate cancer in the screening group, as compared with the control group, was 0.80 (95% confidence interval [CI], 0.65 to 0.98; adjusted P=0.04). The absolute risk difference was 0.71 death per 1000 men. This means that 1410 men would need to be screened and 48 additional cases of prostate cancer would need to be treated to prevent one death from prostate cancer. The analysis of men who were actually screened during the first round (excluding subjects with noncompliance) provided a rate ratio for death from prostate cancer of 0.73 (95% CI, 0.56 to 0.90).

Conclusions PSA-based screening reduced the rate of death from prostate cancer by 20% but was associated with a high risk of overdiagnosis. (Current Controlled Trials number, ISRCTN49127736 [controlled-trials.com] .)

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前立腺癌のスクリーニングの有効性に疑問/PSA 医師の一分/BIGLOBEウェブリブログ
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