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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. |
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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
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The
adjusted detection rate ratio for CIN grade 1 or
higher was 1.01, indicating that the 2 methods were
functionally equivalent. |
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The
detection rate ratio for CIN grade 2 or higher was
1.00 (again, essentially the same). |
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For
detecting CIN grade 3 or higher, the rate ratio
was 1.05 (also equivalent). |
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For
detecting frank cervical carcinoma, however, the
rate ratio was 1.69. |
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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. |
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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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