Old, New Pap Methods Equally Good, Dutch Study Finds
TUESDAY, Oct. 27 -- Traditional Pap tests and the newer liquid-based cytology are equally reliable in screening for cervical cancer, a new study has found.
In the United States, liquid-based cytology testing has all but replaced the traditional Pap test, but in Europe the debate continues over which method is best, according to Dr. Mark Schiffman, a senior investigator at the U.S. National Cancer Institute, co-author of an editorial accompanying the study's publication in the Oct. 28 issue of the Journal of the American Medical Association.
The study's lead researcher, Albertus G. Siebers, from Radboud University Nijmegen Medical Centre in the Netherlands, reflects that debate. "Liquid-based cytology is neither more sensitive nor more specific in detecting cancer," he said. "However, the decision to convert to liquid-based cytology cannot be based on the performance of the method alone, as other arguments also play an important role."
The difference between the two tests is not in the way samples are collected but in how they are treated in the laboratory. In a traditional Pap test, cells are collected and smeared on a slide for evaluation. In liquid-based cytology, the cells are rinsed in a vial of preservation solution.
The advantage of liquid-based cytology is that it also screens for human papillomavirus (HPV), which causes most cervical cancers.
To find out which test was best, the researchers randomly assigned 89,784 women who participated in the Dutch cervical screening program to have either a traditional Pap tests or a liquid-based cytology test.
"The main finding of the study is that we provided strong evidence that a relatively new screening method is not necessarily better than the old way of screening with conventional PAP smears," Siebers said.
The Dutch screening program did not allow use of liquid-based cytology testing until recently, he said, because officials did not have sufficient data comparing it with the conventional method.
"The decision to convert to a new method is a very complex one," Siebers said. "The performance of the method is, of course, imperative, but it is not the only factor. Other things must be considered, [including] screening time, the handling of the specimen, the reduced number of inadequates, the possibility of using residue for further diagnostic procedures such as HPV testing [and] the much more standardized way of handling the material that enables computer-assisted screening."
All these factors should be considered to objectively estimate cost-effectiveness and decide whether a change in screening method should be made, Siebers said.
The study's findings led to Dutch officials deciding to allow use of liquid-based cytology testing, he said.
Schiffman noted that liquid-based cytology is more expensive than the traditional Pap smear, but it is preferred by U.S. laboratories because specimens are easier to handle, and more analyses can be done in a day. In addition, the specimen can be used for HPV testing, which is common in the United States.
But any Pap testing could be on the way out, he said, because the ability to prevent and screen for cervical cancer is changing. "We now have vaccines that are going to keep getting better, and we have HPV testing, which is even more sensitive than Pap smears," Schiffman said. "And new techniques will come along."
He predicted major changes in cervical cancer screening in the next few years, "with the powerful sensitivity of doing HPV testing plus a Pap smear that is optimally done no more than every three years starting at age 30."
But he said it remains to be seen whether women will accept screening every three years after having been accustomed to annual testing. "That's a major change coming," Schiffman said.
Posted: October 2009
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