コクラン分析の著者Dr. Peter C. Gotzscheは、「マンモグラフィ検診に行くのも妥当だが、行かないのも妥当だ」と言う。
米国では40才以降の女性は年１回のマンモグラフィ検診を受けるが、英国では50才以降３年に１回である。米国では過剰に売られている。Dr. Ned Calongeは、早期発見は多くの女性にとって延命効果が得られないかもしれないと言う。
Benefits of Mammogram Under Debate in Britain
By RONI CARYN RABIN
Published: March 30, 2009
The conventional wisdom about breast cancer screening is coming under sharp attack in Britain, and health officials there are taking notice.
Hazel Thompson for The New York Times
Letter Signer Hazel Thornton: "The culture is just that mammography is such a very sensible thing to do, so you chug along and have it done."
They have promised to rewrite informational fliers about mammography after advocates and experts complained in a letter to The Times of London that none of the handouts “comes close to telling the truth” ― overstating the benefits of screening and leaving out critical information about the harms.
What women are not told, the letter said, is that for every woman whose life is saved by breast cancer screening, up to 10 healthy women are given diagnoses ― and, often, surgery ― for a cancer that is so slow-growing it would never have threatened a woman’s life.
“The culture is just that mammography is such a very sensible thing to do, so you chug along and have it done,” said one of the signers, Hazel Thornton, in a telephone interview.
Mrs. Thornton, 75, said she became disenchanted with routine screening more than 15 years ago, after a mammogram identified ductal carcinoma in situ, a noninvasive breast cancer that often does not progress. She had a lumpectomy, but was offered such a confusing array of treatment options that she realized doctors knew little about how aggressively to treat this kind of cancer.
“You don’t know about all the uncertainty until you’re one of the unlucky ones, and it happens to you,” she said.
The idea that mammography may do more harm than good may be alien to many American women. The prevention message has emphasized that screening protects women from breast cancer, and one survey of 479 women found that only 7 percent were aware that some cancers grow so slowly that even without treatment they will not affect a woman’s health.
A 2006 analysis by the Nordic Cochrane Center collaborative, an independent research and information center based in Copenhagen, found that for every 2,000 women age 50 to 70 who are screened for 10 years, one woman will be saved from dying of breast cancer, while 10 will have their lives disrupted unnecessarily by overtreatment. The figures were cited in the letter to The Times.
Julietta Patnick, the director of cancer screening programs for the British National Health Service, said the patient handout was being revised and added that information about overdiagnosis might be added.
But in a telephone interview, she dismissed the Cochrane figures as inaccurate. British studies, she said, show that the ratio of lives saved to lives unnecessarily disrupted is more like one to one.
“We know, from statistics, that there are cancers diagnosed through screening that wouldn’t otherwise have been diagnosed ― because the woman dies of something else first, because she might get run over by a bus, or she might have a heart attack, or she might live to 90 and it would just sit there, and she wouldn’t have died of breast cancer,” Ms. Patnick said.
But the problem is, “You don’t know who that woman is,” she continued. “You just know that statistically, she exists.”
Experts agree that under a microscope, slow-growing cancers look no different from more aggressive ones, so it is impossible to know which ones can be left untouched.
The author of the Cochrane analysis, Dr. Peter C. Gotzsche, another signer of the British letter, has written an alternative version of a patient handout for women considering mammography. It starts off by saying, “It may be reasonable to attend breast cancer screening with mammography, but it may also be reasonable not to attend.”
Women in the United States are screened much more rigorously than women in Britain, with annual mammography starting at 40. British women start at 50, and get a mammogram once every three years.
Dr. Ned Calonge, chairman of the United States Preventive Services Task Force, says mammography has been oversold to American women.
“The expectation of women is that ‘If I get screened, I won’t get breast cancer,’ ” he said. “I hear that women will say: ‘How can I have breast cancer? I always get my mammogram.’ ”
In fact, Dr. Calonge went on, early detection may not make a difference in survival for many women.
“Some women would have the same outcomes, whether the cancer is detected clinically or by mammography,” he said. “And there are women whose cancer is so aggressive we cannot detect it early enough to make a difference in mortality.”
An expert panel that reviewed the evidence on annual mammography for the task force in 2002 downgraded the recommendation for annual screens to “recommended” from “strongly recommended.” That review raised some of the same concerns mentioned by the critics in Britain: the high incidence of false-positive scares that cause anxiety yet turn out to be nothing serious, and the potential overtreatment of ductal carcinoma in situ and other “indolent” cancers. The panel also expressed concern about the potential for harm from exposure to radiation during the scans.
Mammography is more effective in older women. But even among women 50 and over, the panel concluded, only one death would be prevented after 14 years of observing more than 800 women who had undergone screening.
“That’s a hefty number of women” who must be screened to derive a benefit, Dr. Calonge said.
Similarly, studies about prostate screening for men concluded this month that the P.S.A. blood tests save few lives while leading to unnecessary treatment with potentially serious complications.
Despite the task force’s reservations, most medical societies endorse annual mammography, as does the American Cancer Society. Robert Smith, director of cancer screening for the society, says he believes overdiagnosis is minimal at best, and only 10 percent of invasive cancers found through mammography are harmless and will never be life-threatening.
“I think this is another example of, ‘Here is something your doctor knows and isn’t telling you,’ ” Dr. Smith said. “This is a debate between people who see the glass half full or the glass half empty.”
“Breast cancer screening is a good part of a preventive health care plan,” he continued. “It’s not perfect.”
Ultimately, women have to make their own decision about whether to be screened, said Dr. Lisa M. Schwartz, an associate professor at Dartmouth Medical School, who is co-author of “Know Your Chances” (University of California, 2008), a book about how to interpret health statistics and risk.
“You’re not crazy if you don’t get screened, and you’re not crazy if you do get screened,” said Dr. Schwartz, who also signed the letter to The Times. “People can make their own decision, and we don’t need to coerce people into doing this.
“There is a real trade-off of benefits and harms. Women should know that. There’s no question on one count: if you get screened, it’s more likely you’ll have a diagnosis of breast cancer.”
Screening for breast cancer with mammography (Review)
Gotzsche PC, Nielsen M
This record should be cited as:
Gotzsche PC, NielsenM. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006, Issue 4. Art.
No.: CD001877. DOI: 10.1002/14651858.CD001877.pub2.
This version first published online: 18 October 2006 in Issue 4, 2006.
Date of most recent substantive amendment: 12 July 2006
A B S T R A C T
A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.
To assess the effect of screening for breast cancer with mammography on mortality and morbidity.
We searched PubMed (June 2005).
Randomised trials comparing mammographic screening with no mammographic screening.
Data collection and analysis
Both authors independently extracted data. Study authors were contacted for additional information.
Seven completed and eligible trials involving half a million women were identified. We excluded a biased trial from analysis. Two trials with adequate randomisation did not show a significant reduction in breast cancer mortality, relative risk (RR) 0.93 (95% confidence interval 0.80 to 1.09) at 13 years; four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality, RR 0.75 (0.67 to 0.83) (P = 0.02 for difference between the two estimates). RR for all six trials combined was 0.80 (0.73 to 0.88).
The two trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, RR 1.02 (0.95 to 1.10) after 10 years, or on all-cause mortality, RR 1.00 (0.96 to 1.04) after 13 years. We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death.
Numbers of lumpectomies and mastectomies were significantly larger in the screened groups, RR 1.31 (1.22 to 1.42) for the two adequately randomised trials; the use of radiotherapy was similarly increased.
Screening likely reduces breast cancer mortality. Based on all trials, the reduction is 20%, but as the effect is lower in the highest quality trials, a more reasonable estimate is a 15% relative risk reduction. Based on the risk level of women in these trials, the absolute risk reduction was 0.05%. Screening also leads to overdiagnosis and overtreatment, with an estimated 30% increase, or an absolute risk increase of 0.5%. This means that for every 2000 women invited for screening throughout 10 years, one will have her life rolonged.
In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily. It is thus not clear whether screening does more good than harm.Women invited to screening should be fully informed of both benefits and harms.
|<< 前記事(2009/03/31)||ブログのトップへ||後記事(2009/04/02) >>|
|<< 前記事(2009/03/31)||ブログのトップへ||後記事(2009/04/02) >>|