Doctors: Pap remains best test for cervical cancer

By MARILYNN MARCHIONE - AP Chief Medical Writer | AP – Tue, Oct 18, 2011

There's more news on cancer screening tests — this time for women.

Scientists advising the government say a Pap test is a good way to screen young and middle-aged women for cervical cancer, and it's only needed once every three years. But they say there is not enough evidence yet to back testing for HPV, the virus that causes the disease.

That's at odds with the American Cancer Society and other groups, which have long said that using both tests can be an option for women over 30.

Those groups and the U.S. Preventive Services Task Force separately plan to release proposed new guidelines for cervical cancer screening on Wednesday and invite public comment. The task force is the same group that recommended against routine PSA tests to screen for prostate cancer, saying they were doing more harm than good for men at average risk.

Cervical cancer screening is a success story. In the United States, cases and death rates have been cut more than in half since the 1970s because of Pap smears — lab exams of cells scraped from the cervix, the gateway to the uterus. The test can find early signs of this slow-growing cancer and treat them before a tumor has a chance to develop.

So "the bar is set pretty high" for a test to replace or supplement Paps, said Dr. Evelyn Whitlock of Kaiser Permanente Northwest's Center for Health Research in Portland, Ore.

Not enough is known about the benefits and especially the harms of HPV testing, concludes a scientific review she led for the task force that was published on Monday. The panel voted unanimously in March that there was insufficient evidence to recommend for or against HPV testing, but has continued to discuss the issue and will give its advice on Wednesday.

Here's the dilemma: Infections with HPV, the human papillomavirus, are very common especially in young women. They usually go away on their own and only pose a cancer risk when they last a year or more.

Tests that find these infections might lead many women to more invasive follow-up tests that can weaken the cervix and cause problems having children later. No big studies measure these harms, and a test that flags more potential cancers might not be better.

"A lot of people use the word 'superior' to mean it catches more cancer. But the other side of it is, does it catch more things that are not cancer? You have to weigh benefits versus harms for any screening test," said Debbie Saslow, the cancer society's director of breast and gynecologic cancer.

The evidence review finds little risk of cervical cancer in women under 21 and says screening below that age may be harmful. It also says screening can stop at age 65 if a woman has had adequate screening in the past and is not otherwise at high risk.

The review was published Monday in the Annals of Internal Medicine.

The same journal also published a study on another women's cancer issue — breast cancer screening. That research supports having mammograms every other year instead of annually. Over time, there are more false alarms with annual screening, and going every two years does not significantly raise the risk of a late-stage cancer being found, researchers report.

Breast cancer screening has been an emotional issue since 2009 when the government task force said women at average risk of the disease don't need mammograms until age 50 and then just every other year to age 74. The cancer society and others still advise annual tests starting at age 40.

The federally funded study gives a real-world view of the downside of screening — the worry, expense and medical risks of biopsies and other tests that ultimately prove unnecessary. It looked at false alarms at various intervals of screening for nearly 170,000 women ages 40 to 59 in ordinary community settings, plus nearly 4,500 other women with invasive breast cancer.

About 61 percent of women who get a mammogram every year for a decade will be called back at least once for extra tests that turn out not to show breast cancer, the study found.

Screening every other year drops this false alarm rate to 42 percent without a big risk of cancer being discovered at a late stage. And a tip for women: If you changed where you go for mammograms, bringing or having doctors send your last one to be compared to the new one cuts in half the chance of a false alarm.

Women who started having mammograms in their 40s versus their 50s were more likely to have a false alarm just because they were having more tests — not because mammography is less accurate in that age group.

False alarms "are part of the price to pay for early detection," said study leader Rebecca Hubbard of Group Health Research Institute, part of a Seattle-based managed care system. Women need to know how common they are, and "if it happens to them they will feel less anxiety," she said.

Dr. Robert Smith, the cancer society's director of cancer screening, said the study should have more precisely defined intervals — it called annual screening an interval of 9 to 18 months, and biennial screening, 19 to 30 months.

"A false positive is commonly discussed as if it were a catastrophic event. For the large majority of women, it isn't," and surveys say women will accept the risk in return for finding cancer early, he said.

Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP 

子宫颈抹片检查是检验子宫颈癌的最好方式

科学家向政府建议说，子宫颈抹片检查是年轻和中年妇女进行宫颈癌筛查的很好方式。这个筛查只需要每三年做一次。但他们表示还没有足够的证据来肯定HPV（导致子宫颈癌的人乳头状瘤病毒）检测。

这个观点和美国癌症协会还有其他团体不一致，这些团体早就提出对于超过30岁的妇女任一种检测方法都是可取的。

这些团体和美国预防服务工作组分别计划在星期三提出新的子宫颈癌普查方针，并邀请公众给予意见。预防服务工作组也是反对运用常规PSA检查来进行前列腺癌筛查的小组，他们表示这个检查的平均风险是弊大于利的。

宫颈癌筛查是一个成功的案例。子宫抹片检查（在实验室里对宫颈刮片细胞进行检查）的运用，使得美国自20世纪70年代以来，病例和死亡率已经减少了超过一半。这个检查可以发现缓慢发展的癌症的早期征兆并在肿瘤生长的前期及时治疗。

俄勒冈州波特兰市，凯萨医疗机构在西北健康研究中心的Evelyn Whitlock博士表示，要用另一种方式取代或补充子宫抹片检查的要求是非常高的。

目前对于HPV检测的好处与危害还没有足够的了解，这让以Evelyn Whitlock博士为首的工作组在周一的科学报告中发表了这样的观点。专家组在三月的投票中全体一致认为，还没有足够的证据来支持或反对HPV检测，所以会在周三继续讨论这一问题，并给予意见。

现在面临着两难的问题：人类乳头状瘤病毒感染是很常见的，尤其在年轻女性中。人类乳头状瘤病毒只有在持续一年或更多的时间后才会构成癌症的风险。

发现这些感染的检测可能会导致许多妇女要做更多侵入的后续检测，这些后续检查可能会削弱宫颈并在今后引起生育方面的问题。还没有研究测试来估量这些危害，并且如果一个检测的结果意味着可能存在着更多潜在癌症的危险并不是一件好事。

“很多人用‘出色’这个词来形容这个检测的敏锐表现。但另一方面，它可能会检测出更多的问题而不只是癌症。你必须权衡任何筛查的好处与危害。”癌症协会乳腺癌和妇科肿瘤的主任Debbie Saslow说道。

通过以前的研究数据表明，21岁以下的妇女得子宫颈癌的概率很低，而且在21岁以下做宫颈检查是有伤害的。研究还表明如果妇女过去一直做了足够的筛查而且结果没有高危性，那么到了65岁就可以停止继续做检查了。

这个评审已在周一发表在内科医学年鉴中。

同一期杂志上还发表了另一个关于女性癌症的问题---乳腺癌筛查的研究。这项研究支持乳房X光检查每隔一年进行一次，而不是每年都做。研究人员表明，随着时间的推移，每年都进行筛查，其结果会存在更多的误诊，而且每隔一年做一次筛查也不会明显提高晚期癌症不被发现的风险。

自从2009年，乳腺癌筛查一直是一个有争议的问题，政府工作组表示，在平均疾病风险中的女性直到50岁都不需要做乳房X光检查，之后就每隔一年检查一次一直到74岁。而癌症协会和其他协会仍然建议女性应在40岁开始每年都进行检查。

联邦政府资助的研究提供了实际现实的观点来阐述筛查带来的负面的影响---顾虑担心，费用和活检与其他检测的医疗风险，这些影响最终证明是不必要的。在不同筛查间隔内，将近17万40至59岁普通社区的妇女做了乳腺癌筛查，有4500名妇女被误诊为浸润性乳腺癌而虚惊一场。

研究表明，在十年内，每年接受乳房X光检查的妇女中，大约有61%的女性至少要进行一次额外的检测来证明其结果不是乳腺癌。

而筛查定期每隔一年进行一次，误报率可以下降到42％，而且也可以排除癌症发展为晚期的危险。给妇女的提示：你可以换一个地方做乳房X光检查，带好上次医生给你诊断结果，再与新的检查结果相比较，这样可以减少一半误诊的机会。

把那些在40岁开始接受乳房X光检查的女性与50岁开始接受检查的女性相比，40岁开始接受筛查的人更容易被误诊，不是因为这个年龄组的乳房X光检查的准确率低一些，而是因为她们接受了更多的检测。

“误诊误报一部分是过早进行检测的代价。”西雅图管理保健系统卫生研究所的负责人Rebecca Hubbard这样说到，“妇女需要知道误诊是常见的，当遇到这样的情况的时候不要过于焦虑。”

癌症协会筛检主任Robert Smith说，这项研究应该有更精确的时间段来定义，年度筛查有9至18个月的时间段，两年一次的筛查，19至30个月。

“假阳性如同一个灾难性的事件被普遍讨论。但对大部分妇女来说，这不是。”调查表明，“妇女们愿意为了更早的发现或排除癌症而接受风险。”他说。