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Traditional Pap Smears Work as well as ThinPrep Cytology Test for Detecting Precancerous Cervical Cell Changes

SUMMARY: Conventional Pap smears can detect cervical neoplasia, or precancerous cell changes, as well as the newer ThinPrep liquid-based cytology test, indicating that both methods effectively predict cervical cancer, according to a study in the October 28, 2009 Journal of the American Medical Association.

By Liz Highleyman

Women with HIV are at higher risk of human papillomavirus (HPV), which can cause cervical cell changes (dysplasia or neoplasia) leading to cervical cancer. Invasive cervical cancer is an AIDS-defining condition, but HIV positive women are not more likely to die of cervical cancer than HIV negative women, which has been attributed to regular screening that can detect precancerous changes at and early, more treatable stage.

Definition of Cervical cancer
Cervical cancer: Cancer of the entrance to the womb (uterus). The cervix is the lower, narrow part of the uterus (womb). The uterus, a hollow, pear-shaped organ, is located in a woman's lower abdomen, between the bladder and the rectum. The cervix forms a canal that opens into the vagina, which leads to the outside of the body.

In a traditional Pap (or Papanicolaou) test -- used since the 1040s -- the clinician obtains a specimen of cervical cells that are smeared on a slide and examined under a microscope. Using a newer method approved in 1996, known as liquid-based cytology (brand name ThinPrep), cervical cells are rinsed in a preservative solution before examination; the same sample can also be tested for the presence of HPV. Most U.S. gynecologists now use the ThinPrep test.

Investigators from the Netherlands and Belgium conducted a study to assess the performance of liquid-based cytology compared with conventional Pap cytology for detecting histologically confirmed cervical intraepithelial neoplasia (CIN).

This controlled trial included 89,784 women aged 30 to 60 years who participated in a Dutch cervical screening program at 246 family practice facilities. Between April 2004 and July 2006, 122 practices assigned to use liquid-based cytology screened 49,222 patients, while 124 practices assigned to use conventional Pap tests screened 40,562 patients.

Participants were followed for 18 months through the end of January 2008. The main outcome measures were CIN detection rates and positive predictive values using the 2 cytology systems.

Results

The adjusted detection rate ratio for CIN grade 1 or higher was 1.01, indicating that the 2 methods were functionally equivalent.
The detection rate ratio for CIN grade 2 or higher was 1.00 (again, essentially the same).
For detecting CIN grade 3 or higher, the rate ratio was 1.05 (also equivalent).
For detecting frank cervical carcinoma, however, the rate ratio was 1.69.
The adjusted positive predictive value (PPV) ratios, considered at several cytological cutoffs and for various CIN outcomes, did not differ significantly from 1, or equivalence.
1 in 100 Pap smears had to be redone due to errors or unreadability, compared with 1 in 300 liquid-based cytology tests.

Based on these findings, the study authors wrote, "This study indicates that liquid-based cytology does not perform better than conventional Pap tests in terms of relative sensitivity and PPV for detection of cervical cancer precursors."


The researchers demonstrated that "the most common liquid-based cytology method is no better for detection of cervical pre-cancer than well-performed Pap smears," wrote Mark Schiffman and Diane Solomon in an accompanying editorial. "This trial confirms a recent meta-analysis that also showed no incremental improvement in accuracy using liquid-based cytology."

However, they noted, while ThinPrep is more expensive, it "is preferred by most laboratories because the specimen is easier and quicker to scan under the microscope." They also suggested that cervical cytology may fall by the wayside in favor of direct testing for HPV, especially as a growing proportion of women are covered by the recently approved HPV vaccines.

Departments of Pathology and Obstetrics & Gynaecology, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands; Laboratory of Pathology, PAMM Laboratories, Eindhoven, Netherlands; Scientific Institute of Public Health, Brussels, Belgium.

10/30/09

References

AG Siebers, PJ Klinkhamer, JM Grefte, and others. Comparison of Liquid-Based Cytology With Conventional Cytology for Detection of Cervical Cancer Precursors: A Randomized Controlled Trial. Journal of the American Medical Association 302(16): 1757-1764. October 28, 2009. (Abstract).

M Schiffman and D Solomon. Screening and Prevention Methods for Cervical Cancer (editorial). Journal of the American Medical Association 302(16): 1809-1810. October 28, 2009.

Other Source

M Szalavitz. Newer Isn't Always Better: Pap Smear Version. Time magazine Wellness blog. October 28, 2009.



 




 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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